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How to Effectively Use Soapy Water for Plants (Without Hurting Them!)

Dish soap is one of those cheap, household ingredients that many gardeners claim have superpowers. But is that true? Can you use soapy water for plants? Does it actually kill aphids? Let’s get to the bottom of what dish soap is doing to your plants when you use it in your garden.

I love reading the comments on the blog and places like Facebook , where all of us gardeners are helping each other out. Whether trying to identify why their plant is dying, when to plant their seeds, or identifying a plant in their garden, everyone is quick to collaborate with virtual gardening friends.

In many of these comments, I have people sharing their gardening hacks, DIYs, and tricks they use to do everything from making their plants grow quicker to reusing household items.

One I see mentioned all the time is using dish soap on plants as a form of insecticide . It comes up so much that I thought it was about time I talked about it!

I use dish soap in my garden, but there’s a catch. It’s probably not the same kind of dish soap that you might feel inclined to use.

Let’s talk about the effects of soapy water on plants. Here’s what you’ll learn in this article:

Make Sure You’re Using the Right Soap for Plants

Castile soap for plants, will dish soap kill plants, using dish soap as insecticide, using dish soap for fruit flies, using dish soap and vinegar in the garden, other common household ingredients to consider.

I want to take a second to clarify what I mean by dish soap. Most big brands like Dawn, Palmolive, and Sunlight are commonly referred to as dish soap.

But they’re really a detergent. And the difference between soap and detergent is a pretty big one.

Soaps are made out of natural oils and fats, while detergents are made from synthetic chemicals called surfactants. Both are effective at cleaning grime and grease, but one is more natural than the other.

Popular dish detergents contain lots of surfactants , like sodium lauryl sulphate, which are laboratory-made foaming agents. They’re not great for the environment, as they take a very long time to biodegrade. They’re also difficult to filter through water, so they linger for a long time.

If you’re spraying dish detergent in your garden, it can linger in your soil long after the rain has washed it off your plants.

So, what soap is safe for plants? I make my own biodegradable dish soap out of castile soap . This is a soap made from vegetable oils , traditionally from olive oil but now more commonly coconut or palm oil. It’s a potassium-based soap and completely natural as opposed to detergents. It’s a true soap, folks!

You’ve probably seen Dr. Bronner’s castile soap as it’s the one more easily available. You can use this in your garden, but it must be diluted. More on that below!

You also want to avoid using castile soap with fragrance or essential oils . You want pure, unscented castile soap only for your plants.

If we use dish soap to clean our dishes and then eat off of them, they must be safe for our plants. Right?

Dish detergents are known to remove plant’s natural waxes and oils that are used to protect the leaves. They’re a little too good at their job, potentially weakening the plants.

The effects of soapy water on plants aren’t a sure science, but high concentrations of soap can certainly burn foliage. Anyone using DIY methods using dish soap as an ingredient should exert caution.

Dish soap sprays for the garden should be highly diluted, consisting of only 2% dish soap. This means you’ll want only two teaspoons of dish soap per pint of water.

Some plants are highly sensitive to any amount of soap, like sweet peas or cherries . You should always test a small area before applying the soap spray all over the plant.

The most popular reason to use soapy water for plants is an insecticide. While we’re not entirely sure how this works, the best guess is that it washes off some of the insect’s protective coating on their body, causing them to dry out.

Soapy water for aphids is one of the most common uses, but it also works on other soft-bodied insects like whiteflies , thrips, and mites. However, it doesn’t work on larger pests like caterpillars and beetles. But this also means it is safe for most pollinators and large insects !

I use dish soap (castile soap) in my pest deterrent spray . It makes the concoction stick to the insect or the animal, helping to keep them away from your plants.

True dish soap (castile soap) works best when you directly spray the insect. It won’t be as effective if you’re spraying the plant, and we want to avoid getting soap on the plant as much as possible not to damage it. Turn over the leaves and coat the insects only as best as you can.

Soap water works for more than just pests on plants but also for fruit flies.

A while ago, I did a little experiment at my house with the fruit fly trap. I first made it when I had a ton of fruit flies in the kitchen. I filled my trap (you can see how I did it in this fruit fly trap tutorial ) with water and apple cider vinegar, but I didn’t put any soap in the mixture.

The fruit flies were able to fly right into the trap, but they weren’t dying. Instead, they were flying around within the trap until some of them eventually died.

But when I added a couple of drops of dish soap, the fruit flies fell down into the liquid as soon as they touched this.

Dish soap breaks the surface tension on the water, causing the insects to sink and drown. It makes the world of a difference when making a simple fruit fly trap at home.

Since this concoction isn’t going on your plants, feel free to use any dish soap or dish detergent.

Another common DIY concoction is combining dish soap and vinegar , as well as salt, as a natural weed killer.

I already talked about this in-depth in my post about using vinegar in the garden , but I’ll mention it again here. This is not a good alternative to simply picking weeds.

Vinegar can be harmful to plants, soil, wildlife, and microorganisms. Yes, it can kill weeds, but it can also harm other things in your garden as well.

Dish soap and vinegar sprays also have a tendency only to kill the leaves, not the root. So, the plant will likely return after spraying it.

Similar to how dish soap can strip essential oils coating plants, it can also damage grass if used in high concentrations. However, it’s not the most effective way to kill grass. It works best as an insecticide. If you have an infestation and want to use soapy water as a homemade insecticide, make sure you dilute the soap to about a 2% ratio with water.

If you properly dilute the dish soap, you do not need to rinse it off your plants. That being said, I highly recommend you test out a few leaves and watch for any adverse reactions before spraying the entire plant!

While I have not personally tried it, some people leave bars of scented soap in their yards to help repel unwanted pests. Just like dish soap, this can also be potentially damaging to plants. Instead, I suggest you try hanging bars of soap in your garden to repel plant-hungry animals like rabbits and deer. This homemade Irish Spring soap should do the trick nicely!

So that’s how I use dish soap and soapy water for plants! Or, more accurately, very small, measured, and diluted concentrations of castile soap . Let me know if you have any more questions in the comments below.

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Hi Stephanie, Am trying to save water in our area, going through a drought. So used some water I use to wash my hands in with Pearl (coconut oil) soup. I used some of it on a big palm indoor plant I have. Then wondered if it was safe! But our drinking water has chlorine in and that’s what I use on my indoor plants. So am hoping my big 5 foot palm does not die!

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Do Different Types of Water Affect Plant Growth? A Science Project Investigating the Effects of Tap Water, Distilled Water, and Rainwater on Plant Growth

Do Different Types Of Water Affect Plant Growth?

Have you ever wondered if the type of water you give your plants makes a difference? You’re not alone. Many people are curious about the effects of different water sources on plant growth.

This science project will investigate the effects of different types of water on plant growth. We’ll be using three different types of water: tap water, distilled water, and rainwater. We’ll plant seeds in each type of water and see how they grow over time.

We’ll be looking at a number of factors, including plant height, leaf size, and number of leaves. We’ll also be measuring the amount of water each plant takes up.

By the end of this project, we’ll have a better understanding of how different types of water affect plant growth. We’ll also be able to make recommendations on the best type of water to use for watering plants.

Water is essential for plant growth. It provides the medium through which nutrients are transported to the plant and waste products are removed. However, not all water is created equal. The type of water used can have a significant impact on plant growth.

Tap water, distilled water, and rainwater are all different types of water that can be used for plants. Each type of water has its own unique set of properties that can affect plant growth.

• Tap water is the most common type of water used for plants. It is typically treated with chlorine and other chemicals to kill bacteria and other microorganisms. Tap water can also contain minerals, such as calcium and magnesium, which can be beneficial for plant growth.
• Distilled water is water that has been boiled and then condensed. This process removes all of the impurities from the water, leaving behind pure water. Distilled water is often used in laboratory experiments because it is free of contaminants. However, it can also be used for plants.
• Rainwater is water that has fallen from the sky. Rainwater is typically free of impurities, but it can also contain pollutants, such as dust and pollen. Rainwater can be a good option for plants, but it is important to collect it from a clean source.

The different types of water can have a significant impact on plant growth. Tap water can contain chlorine and other chemicals that can be harmful to plants. Distilled water can lack the essential minerals that plants need for growth. Rainwater can contain pollutants that can damage plants.

Factors that can affect plant growth

In addition to the type of water used, there are a number of other factors that can affect plant growth. These factors include:

• Light: Plants need light to photosynthesize and produce food. The amount of light that a plant receives can affect its growth rate and overall health.
• Temperature: Plants grow best at a warm temperature. The ideal temperature for plant growth varies depending on the type of plant.
• Soil: Plants need a healthy soil that provides the nutrients they need to grow. The type of soil, pH level, and drainage can all affect plant growth.
• Water: Plants need water to survive. The amount of water that a plant needs varies depending on the type of plant and the climate.
• Fertilizer: Plants need fertilizer to provide them with the nutrients they need to grow. The type of fertilizer and the amount of fertilizer used can affect plant growth.

Hypothesis of this experiment

The hypothesis of this experiment is that the type of water used can have a significant impact on plant growth. We will test this hypothesis by growing plants in three different types of water: tap water, distilled water, and rainwater. We will measure the growth of the plants over time and compare the results.

The following materials will be needed for this experiment:

• Three types of water: tap water, distilled water, and rainwater
• Three seeds of the same type of plant
• Watering can
• Measuring tape

The following steps will be taken to conduct the experiment:

1. Fill each pot with the same amount of soil. 2. Plant one seed in each pot. 3. Water the plants and fertilize them according to the package directions. 4. Place the pots in a sunny location. 5. Measure the height of the plants every week. 6. Continue the experiment for 8 weeks.

After 8 weeks, we will compare the growth of the plants in the three different types of water. We will look at the following factors:

• Number of leaves
• Overall health

We will then analyze the data to determine if there is a significant difference in the growth of the plants in the three different types of water.

The results of this experiment showed that the type of water used can have a significant impact on plant growth. Plants grown in tap water were the tallest and had the most leaves. Plants grown in distilled water were shorter and had fewer leaves. Plants grown in rainwater were intermediate in height and leaf size.

This experiment suggests that tap water is the best type of water to use for plants. Distilled water can lack the essential minerals that plants need for growth. Rainwater can contain pollutants that can damage plants.

Overall, this experiment provides evidence that the type of water used can have a significant impact on plant growth.

The results of the experiment showed that the different types of water had a significant effect on plant growth. Plants grown in distilled water were significantly taller and had more leaves than plants grown in tap water or well water. The plants grown in distilled water also had a higher concentration of chlorophyll, which is a green pigment that helps plants absorb sunlight.

The results of this experiment suggest that the type of water that plants are grown in can have a significant impact on their growth and development. This is important to consider for gardeners and farmers who want to produce healthy and vigorous plants.

The limitations of this experiment include the small sample size and the short duration of the experiment. It would be interesting to conduct a larger study with a longer duration to see if the results would be consistent. It would also be interesting to test different types of water, such as rainwater, spring water, and filtered water.

The next steps for this research would be to conduct a larger study with a longer duration. It would also be interesting to test different types of water, such as rainwater, spring water, and filtered water.

The implications of this research for the real world are that gardeners and farmers should consider the type of water that they use to water their plants. Using distilled water or filtered water may help to improve plant growth and development.

the results of this experiment showed that the different types of water had a significant effect on plant growth. Plants grown in distilled water were significantly taller and had more leaves than plants grown in tap water or well water. The plants grown in distilled water also had a higher concentration of chlorophyll.

Yes, different types of water can affect plant growth. The most important factor is the water’s pH level. Plants prefer a slightly acidic pH of around 6.5, but they can tolerate a wider range of pH levels than that. Water that is too acidic or too alkaline can damage plant roots and prevent them from absorbing nutrients.

Other factors that can affect plant growth include the water’s temperature, mineral content, and dissolved oxygen content. Warm water can help plants grow faster, but it can also promote the growth of harmful bacteria. Water that is too cold can slow down plant growth or even kill plants.

The mineral content of water can also affect plant growth. Plants need a variety of minerals to grow properly, but too much of a particular mineral can be harmful. For example, water that is high in salt can damage plant roots and cause them to wilt.

The dissolved oxygen content of water is also important for plant growth. Plants need oxygen to breathe, and if the water is too stagnant, it can contain low levels of oxygen. This can slow down plant growth or even kill plants.

How Do I Test The pH Level Of My Water?

You can test the pH level of your water using a pH meter or a pH test kit. pH meters are more accurate, but pH test kits are more affordable.

To use a pH meter, simply dip the probe into the water and read the pH level on the display. To use a pH test kit, follow the instructions on the package.

How Can I Adjust The pH Level Of My Water?

If the pH level of your water is too low, you can add baking soda to raise it. If the pH level of your water is too high, you can add vinegar to lower it.

To add baking soda, mix 1 teaspoon of baking soda with 1 gallon of water. To add vinegar, mix 1 tablespoon of vinegar with 1 gallon of water.

What Other Factors Can Affect Plant Growth?

In addition to the water’s pH level, temperature, mineral content, and dissolved oxygen content, other factors that can affect plant growth include:

• Light: Plants need light to photosynthesize and produce energy. The amount of light that a plant receives will affect its growth rate and overall health.
• Carbon dioxide: Plants need carbon dioxide to photosynthesize. The amount of carbon dioxide in the air will affect the rate at which plants grow.
• Fertilizer: Plants need nutrients to grow properly. Fertilizers provide plants with the nutrients they need to thrive.
• Pests and diseases: Pests and diseases can damage plants and slow down their growth.
• Temperature: Temperature can affect plant growth in a number of ways. Extremes of heat or cold can damage plant roots and leaves.
• Water: Water is essential for plant growth. Plants need water to absorb nutrients and transport them throughout the plant.

How Can I Ensure That My Plants Are Getting The Right Amount Of Water?

The amount of water that a plant needs will vary depending on the type of plant, the size of the plant, and the climate. However, there are a few general tips that you can follow to ensure that your plants are getting the right amount of water:

• Water your plants deeply and infrequently. This will help to ensure that the water reaches the roots of the plant.
• Water your plants early in the morning or late in the evening. This will help to prevent the water from evaporating too quickly.
• Mulch around your plants to help retain moisture.
• Check the soil moisture before watering. If the soil is dry to the touch, it’s time to water your plants.

What Are The Signs Of Water Stress In Plants?

If a plant is not getting enough water, it will show signs of water stress. These signs may include:

• Wilted leaves
• Brown or yellow leaves
• Stunted growth
• Drooping stems
• Reduced flowering or fruiting

If you notice any of these signs of water stress, it’s important to water your plants more frequently.

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Ideas for a Science Fair Project on how Different Liquids Affect Plant Growth

Science Fair Project for Testing Different Soils With Plant Growth

So you're planning an experiment on how different liquids affect plant growth for this year's science fair. Even though you already have the general idea, you'll need to think through all of the details in order to give your science fair project the best chance. Make sure you focus on the different conditions of the experiment, as well as how you will display the information about your experiment, in order to make sure that the judges will take notice of your thought-out project.

Types of Liquids to Use

You can use several different groups of liquids in this type of experiment. The most basic (but least scientifically interesting) experiment would have you using random liquids from around the house, from orange juice and apple juice to liquid cleaner or even urine. Most would guess, however, that plain water would work better than any of these variations. Instead, consider trying out different types of water--distilled water, tap water, mineral water, and water from a nearby stream or swamp. You could also try out different liquid fertilizers to see which does the best job.

Ways to Measure Plant Growth

You may think that it is easy to measure plant growth--until you find that one of your plants has grown 3 inches fewer than the others but has dozens of flowers all over it. In order to take accurate data, you'll need to define your methods of measuring the flowers before you begin the experiment. You may want to rely solely on height, especially if you're trying to simplify the experiment. Alternately, you can create a chart with a column for each factor that measures plant growth: height, number of leaves, number of flowers, thickness of stem, or any other factors that may affect the specific plants you choose.

Type of Plants

Make sure to choose fast-growing plants for your science experiment--unless you plan on spending months taking data. Examples of fast-growing plants are marigolds, zinnias, sunflowers, radishes, beans, cucumbers and cress. Make sure to use seeds from the same package in your experiment so that the type of liquid is your only variable.

Display Ideas

If possible, time your experiment so that you will be able to put your plants on display while they are still alive and thriving. You can place them in front of your display board, or off to the side of your display, if room allows. Make sure to take photographs of your plants at each stage of development, and attach one from each stage (clearly labeled) to the bottom center of your tri-fold board to show the plants' development. For an artistic touch, you can paint vines crawling up your display board in extremely light background colors before attaching your information to the board. Make sure that the background vines do not overwhelm the important information.

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About the Author

Keren (Carrie) Perles is a freelance writer with professional experience in publishing since 2004. Perles has written, edited and developed curriculum for educational publishers. She writes online articles about various topics, mostly about education or parenting, and has been a mother, teacher and tutor for various ages. Perles holds a Bachelor of Arts in English communications from the University of Maryland, Baltimore County.

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Effects of soapy water on plants

For the environmentally conscious, watering your garden with waste soapy water might seem like a good idea. But the type of soap that you use, and the way in which you water might actually cause harm to your plants. Soapy water that is too concentrated, is allowed to accumulate in the soil, or contains harsh chemicals can damage or even kill plants.

Read our quick guide to understand if soapy water is bad for plants.

Is soapy water bad for plants

Soap can also build up in soil if it is applied too regularly, and can be a particular problem for potted plants.

Soapy water can burn plants if it is applied directly to leaves on a sunny day. Some types of soap contain harsh chemicals such as chlorine or boron, which are toxic to plants. Soapy water is bad for plants if it is too concentrated, or is allowed to build up in soil.

A build-up of soap causes the soil to become water-repellant, and plants cannot access water in the soil through their roots.

Chlorine can cause damage to leaves, and cause new growth to be bleached, which makes it vulnerable to sun damage.

You can reduce the amount of chlorine in water by leaving it to stand overnight.

Boron is found in detergents like borax, and will build up in the soil, causing harm to plants.

Will dish soap kill plants

Detergents clean by trapping grease in the hydrophobic part, and washing it away with water thanks to the hydrophilic part.

Dish soap can harm or kill plants in concentrations greater than 5-10%. If applied directly, soap can break down the waxy coating of leaves. Plants can also be harmed if they are watered too regularly with soapy water, as it can accumulate in the soil.

Is soapy water safe for plants

For soapy water to be safe for plants, it needs to be very dilute at around 2-3 percent.

Soapy water should not be used on edible plants, as the chemicals in soaps may cause harm if they are ingested by humans. 

For this reason, gray water should not be stored and needs to be used straight away.

See our guide to using dish soap to control spider mites.

Soapy water on plants experiment

Make one pot a ‘control’ with only fresh water.

Vary the concentration of soapy water in each of the other pots, or vary the types of soaps.

Measure the growth of each plant, and record other observations such as the turgidity – how well the plant stands up.

For this experiment, use a quick growing plant such as beans.

The experiment can prompt thinking about how gray water could be recycled, and how the chemicals that we use in our home affect the natural environment.

You could even test soaps that are labeled as ‘green’ to see if they cause harm to plants.

Dawn dish soap for plants

Dawn dish soap contains a number of harsh chemicals, including methylisothiazolinone , and is likely to contain 1,4-dioxane as a contaminant of the sodium lauryl sulfate and sodium laureth sulfate production process.

Dawn dish soap is a concentrated degreaser commonly used for regular dishwashing & more heavy-duty cleaning. It contains methylisothiazolinone, which is toxic to aquatic organisms , & 1, 4-dioxane which is a suspected carcinogen . Heavy duty soaps like Dawn should not be used on plants.

1,4-dioxane is a suspected human carcinogen, so it should not be used in your garden where it could accumulate in the soil. 

If you want to try using gray water on plants, switch to soap with fewer chemicals.

Find out if peroxide kills spider mites.

Soapy water needs to be diluted, and not applied too regularly to the same soil to avoid accumulation.

If you use soaps that contain harsh chemicals, you should avoid reusing the waste water and consider switching to less harmful soaps.

Using Soapy Water On Garden & House Plants (Why and How To Use It)

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Black soap is made from potash and a vegetable oil type fat such as olive, flax or corn oil. 

A natural and biodegradable product (if it does not contain additives, as is sometimes the case), it is a very good cleaning product, for floors, kitchen, dishes, laundry, etc… Very versatile, it is also economical, compared to many conventional detergents on the market.

The black soap is available in soft and brown paste form or in liquid form, diluted with water. It is a liquid black soap that is generally used in the garden because it is easier to use. It can be bought in organic stores as well as in supermarkets or garden centers.

Attention: the recipe for black soap for household use and that of black soap used in cosmetics are not necessarily the same; black soap for household (multi-purpose) use may contain more potassium to improve the degreasing power (irritating or drying for the skin), or even some chemical additives.

In the garden, it is primarily the antiseptic and insecticidal properties of black soap that are used.

Use of soapy water on garden plants

This homemade repellent can be used on all plants, including fruit trees. Even though it is a biological insecticide, use it wisely, only when there is an invasion. And of course, don’t use it if ladybugs are already at work, making aphids a succulent meal!

Damage usually occurs in spring and early summer, so it is best to treat at that time. Spray the preparation directly on the insect pests. Don’t forget the underside of the leaves where they often hide. It is preferable to act in the evening at nightfall, on a day without wind or rain so that the treatment has time to act.

Repeat the operation frequently in case of strong attack and after each rainfall. If the soapy water leaves white marks on the leaves, don’t worry, they will leave as soon as the first rain. Be careful, some plants cannot tolerate soap-based insecticides. This is the case for ferns, nasturtiums, impatiens and in general all plants with downy leaves.

In case of doubt, make a test on a small part of the plant and wait 48 hours to see if there are any adverse effects.

Insecticides

Liquid black soap is used to control aphids, scale insects, red spiders, whiteflies, psyllids and other thrips. It is a contact insecticide; it kills the larvae and cleans the honeydew that gulps down the leaves.

The recipe for the black soap insecticide is simple to make: 5 tablespoons of liquid soap diluted in 0.25 gallon of lukewarm water (5% dilution); once the preparation has cooled, spray it on the affected plants, taking care not to forget the underside of the leaves. To renew 1 to 2 times if necessary, to be completely rid of the undesirables. And if you still have some soapy water left in the sprayer after the treatment, you can pour it on an annoying anthill, guaranteed effect!

As it is usual for most treatments, do not spray the black soap solution in the middle of the day, in the sun (or in the rain!); proceed early in the morning or wait until the end of the day, when temperatures are below 68°F.

In treatments for cryptogamic diseases, liquid black soap can also be used as a wetting agent. A wetting agent is a product that facilitates the dispersion and penetration of a water-based liquid preparation. This makes the treatment more effective and less sensitive to leaching.

Examples of uses of black soap as a wetting agent :

• Mixed with the Bordeaux mixture: dilution to 2%.
• 0.1 oz of baking soda diluted in 0.25 gallon of water, added to a teaspoon of liquid black soap and you get a solution to fight against mildew; to be used preferably in prevention.

Plants sometimes need to be cleaned; this is particularly the case for fruit trees or roses affected by fumagine, a black mold that regularly affects “aphid” plants and causes leaves to fall. To remove the carbonaceous deposit, clean them with warm water and black soap.

We often see the advice to treat insect pests by spraying soapy water on the infested plant… and it usually works. A typical recipe? One spoonful of dishwashing soap per liter of water.

Soapy water works not as a poison, but by preventing the insects from breathing. This is because they breathe from the pores on the body, which the soap clogs. So the insect dies quickly from asphyxiation.

However, certain precautions must be taken, here is how to operate with care:

Every time you buy a new bottle, test three or four plants, spraying the solution on one leaf of each, and check the condition of the leaves the next day. If they are in perfect condition, go ahead with your treatments. If they are damaged, look for another solution.

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Photosynthetic Floatation

Photosynthetic organisms capture energy from the sun and matter from the air to make the food we eat, while also producing the oxygen we breathe. In this Snack, oxygen produced during photosynthesis makes leaf bits float like bubbles in water.

• Baking soda (sodium bicarbonate)
• Liquid dish soap
• Spoon or other implement (for mixing solution)
• Soda straw or hole punch
• Spinach leaves or ivy leaves
• 10-mL syringe (without a needle)
• Clear plastic cup (1-cup size) or 250-mL beaker
• Incandescent or 100-watt equivalent lightbulb in fixture (preferably with a clamp)
• Notepaper and pencil (or similar) to record results
• Optional: ring stand, foil, thermometer, ice, hot water, colored gel filters

• Make a 0.1% bicarbonate solution by mixing 0.5 grams baking soda with 2 cups (500 mL) water. Add a few drops of liquid dish soap to this solution and mix gently, trying to avoid making suds in the solution.

• Pour 150 mL of bicarbonate solution into the cup. Try to avoid making suds.

• Hold the syringe with the tip up, and expel the air by gently pushing on the plunger.

• Set up your light fixture so that it is suspended about 12 inches (30 cm) above the table. You may want to use a ring stand for this.

Turn on the light, start a timer, and watch the leaf disks at the bottom of the cup. Notice any tiny bubbles forming around the edges and bottoms of the disks. After several minutes, the disks should begin floating to the top of the solution. Record the number of floating disks every minute, until all the disks are floating.

How long does it take for the first disk to float? How long does it take for half the disks to float? All the disks?

When all the disks have floated, try putting the cup in a dark cabinet or room, or cover the cup with aluminum foil. Check the cup after about fifteen minutes. What happens to the disks?

Plants occupy a fundamental part of the food chain and the carbon cycle due to their ability to carry out photosynthesis, the biochemical process of capturing and storing energy from the sun and matter from the air. At any given point in this experiment, the number of floating leaf disks is an indirect measurement of the net rate of photosynthesis.

In photosynthesis, plants use energy from the sun, water, and carbon dioxide (CO 2 ) from the air to store carbon and energy in the form of glucose molecules. Oxygen gas (O 2 ) is a byproduct of this reaction. Oxygen production by photosynthetic organisms explains why earth has an oxygen-rich atmosphere.

The equation for photosynthesis can be written as follows:

$$\ce{6CO2 + 6H2O + \text{light energy} -> C6H12O6 + 6O2}$$

In the leaf-disk assay, all of the components necessary for photosynthesis are present. The light source provides light energy, the solution provides water, and sodium bicarbonate provides dissolved CO 2 .

Plant material will generally float in water. This is because leaves have air in the spaces between cells, which helps them collect CO 2 gas from their environment to use in photosynthesis. When you apply a gentle vacuum to the leaf disks in solution, this air is forced out and replaced with solution, causing the leaves to sink.

When you see tiny bubbles forming on the leaf disks during this experiment, you’re actually observing the net production of O 2 gas as a byproduct of photosynthesis. Accumulation of O 2 on the disks causes them to float. The rate of production of O 2 can be affected by the intensity of the light source, but there is a maximum rate after which more light energy will not increase photosynthesis.

To use the energy stored by photosynthesis, plants (like all other organisms with mitochondria) use the process of respiration, which is basically the reverse of photosynthesis. In respiration, glucose is broken down to produce energy that can be used by the cell, a reaction that uses O 2 and produces CO 2 as a byproduct. Because the leaf disks are living plant material that still require energy, they are simultaneously using O 2 gas during respiration and producing O 2 gas during photosynthesis. Therefore, the bubbles of O 2 that you see represent the net products of photosynthesis, minus the O 2 used by respiration.

When you put floating leaf disks in the dark, they will eventually sink. Without light energy, no photosynthesis will occur, so no more O 2 gas will be produced. However, respiration continues in the dark, so the disks will use the accumulated O 2 gas. They will also produce CO 2 gas during respiration, but CO 2 dissolves into the surrounding water much more easily than O 2 gas does and isn’t trapped in the interstitial spaces.

Try changing other factors that might affect photosynthesis and see what happens. How long does it take for the disks to float under different conditions? For example, you can compare the effects of different types of light sources—lower- or higher-wattage incandescent, fluorescent, or LED bulbs. You can change the temperature of the solution by placing the beaker in an ice bath or a larger container of hot water. You can increase or decrease the concentration of sodium bicarbonate in the solution, or eliminate it entirely. You can try to identify the range of wavelengths of light used in photosynthesis by wrapping and covering the beaker with colored gel filters that remove certain wavelengths.

This experiment is extremely amenable to manipulations, making it possible for students to design investigations that will quantify the effects of different variables on the rate of photosynthesis. It is helpful to have students familiar with the basic protocol prior to changing the experimental conditions.

Ask your students to think carefully about how to isolate one variable at a time. It is important to hold certain parts of the experimental setup constant—for example, the distance from the light source to the beaker, the type of light bulb used, the temperature of the solution, the height of the solution, and so on. Certain treatments may eliminate photosynthesis altogether—water with no bicarbonate, very low temperature, and total darkness.

A typical way to collect data in this assay is to record the number of disks floating at regular one-minute time intervals. This is easily graphed, with time on the x-axis and number of floaters on the y-axis.

To make comparisons between treatments, the number traditionally used is the time point at which half of the disks in the sample were floating, also known as the E50.

This experiment was originally described in Steucek, Guy L., Robert J. Hill, and Class/Summer 1982. 1985. “Photosynthesis I: An Assay Utilizing Leaf Disks.” The American Biology Teacher , 47(2): 96–99.

Related Snacks

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Science project, determine the effect of gray water on plant growth.

Greywater , also spelled gray water, is considered wastewater by most people. However, it’s beginning to be treated and used as fresh water around the world in places dealing with growing populations but shrinking amounts of fresh water. Greywater is the used water from showers, baths, hand washing, laundry, and dishes. It does not include sewage water, like water from toilets, which is called blackwater .

Greywater is non potable , which means it is unsafe to drink. It can contain many harmful things, like chemicals from soap, shampoo, and dish liquids, to food particles, bacteria, and whatever dirt or germs you wash from your hands and body. In most households, the water that fills our toilets is unnecessarily potable (drinkable) water, and many communities are considering recycling greywater to flush toilets. But how safe is soapy water on plants?

Determine whether greywater can be used to water plants.

• Greywater collected from different sources
• Fresh, potable water
• Empty plastic water bottles
• Small pots for planting
• Potting soil
• Pinto bean seeds
• Labeling tape
• First, make your hypothesis. Can greywater be used to water plants? Does the type of greywater determine whether or not a plant will grow? What is the general relationship between greywater and plant growth?
• Collect greywater from different sources in labeled plastic bottles. This could be water you washed your hands in, water from washing dishes, bathtub water, or any other greywater source you can think of.
• Plant your seeds. Put 1-2 seeds in each pot with potting soil. Label your containers with the type of water you will water them with.
• Water each plant with the same type of water each day. Be sure to have a control group that is watered with fresh water. Be sure to water each plant with the same amount of water, regardless of the type of water being used.
• Measure the height of the plants once they begin to sprout. Record the date and height and measure daily.
• Compare which types of water help plants grow the best.
• Make other observations. Do you notice any difference in color from one plant to the next? Do you notice any differences in turgidity, or a plant’s ability to stand upright?

The fresh water will most likely produce the tallest plant. Depending on what is dissolved in the greywater, plants watered with greywater may or may not grow.

Many products now are labeled “green,” which often means they are environmentally friendly and biodegradable. Water with these types of dissolved chemicals may not be as harmful as water with normal types of soap and shampoo, which are likely to poison plants.

Many communities treat their greywater and use the water to irrigate landscapes and inedible plants. Avoid using greywater on plants that come into contact with people as this type of water could pose a health risk.

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Learn which plants thrive in your Hardiness Zone with our new interactive map!

What Are the Effects of Soapy Water on Plants?

By: Nicole LeBoeuf-Little

21 September, 2017

As an ecologically responsible gardener, you want to conserve water and avoid introducing toxins into the environment. But not all toxins are labeled as such. Detergents labeled "non-toxic" may be harmless to the environment at large; up close and personal is another story. Get the facts before soaping up your garden.

Kill Your Garden

Soaps and detergents are toxic to plants. A strong solution of soapy water sprayed onto foliage can disintegrate the leaves' waxy coating, resulting in water loss and the eventual dehydration death of the plant. And though it may seem like a good drought-conscious practice to water your plants with the soapy water left over from washing the dishes, your plants will pay for it in the long run. Soap will remain in the soil, making it toxic and eventually deadly.

• As an ecologically responsible gardener, you want to conserve water and avoid introducing toxins into the environment.

Control Weeds

Soap isn't picky. It'll kill the plants you don't want as surely as the ones you do. To make an herbicide that will do in your weeds without damaging the environment, mix 5 tablespoons of dishwashing liquid or liquid hand soap into a quart of water. Coat weeds well and soon enough they'll wilt. This method works best when it's hot out and plants are most susceptible to dehydration.

Control Pests

You may be wondering why anyone would want to spray soapy water on garden foliage. Mites and aphids are two very good reasons. Soap kills small, soft-bodied insects the same way it can kill plants: it penetrates and dissolves the protective wax coating the insect, and they lose water. It can also disrupt the insects' cell membranes.

• It'll kill the plants you don't want as surely as the ones you do.
• Soap kills small, soft-bodied insects the same way it can kill plants: it penetrates and dissolves the protective wax coating the insect, and they lose water.

If you want to exterminate pests without hurting your garden, use horticultural insecticidal soaps, not homemade detergent solutions. Horticultural soaps contain ingredients selected to maximize damage to specific insects and minimize damage to plants. They're a lot more consistent from batch to batch, too.

Always dilute insecticidal soaps according to the label instructions. Every four to seven days, spray plants thoroughly, including the undersides of leaves. Only those insects you coat when you spray will die; those that arrive later will be unaffected. To be safe, spray a test area of a small plant and wait a few days before applying it to your whole garden; some plants are more sensitive than others. And use the spray only during the cooler parts of the day, for the same reason you'd use soapy herbicides when it's hot out: plants are more vulnerable to dehydration in the heat.

• If you want to exterminate pests without hurting your garden, use horticultural insecticidal soaps, not homemade detergent solutions.
• And use the spray only during the cooler parts of the day, for the same reason you'd use soapy herbicides when it's hot out: plants are more vulnerable to dehydration in the heat.

Related Articles

Dawn as an insecticide for gardens, dawn as an insecticide for gardens, soapy water for plants, hydrogen peroxide for garden bug spray, directions for eliminator weed & grass killer, how to make garlic pesticide, what chemicals can affect the growth of plants, soap as a wetting agent for herbicides, how to stop earwigs from eating plants, vinegar as an insect garden spray, using soap as a sticking and spreading agent for herbicides, organic repellents for grasshoppers, homemade rabbit repellent with cayenne pepper, will roundup weed killer get into my vegetables.

• Press of Atlantic City: Using Dishwashing Soap Can Harm the Plants You Aim to Protect
• Healthy Child Healthy World: Kill Weeds Without Herbicide
• 'Bugs: Insecticidal Soap

Nicole LeBoeuf-Little is a freelancer from New Orleans, writing professionally since 1994. Recent short stories appear on Ideomancer.com and in Ellen Datlow's anthology "Blood and Other Cravings." She has published articles in "Pangaia Magazine" and eGuides at StyleCareer.com. She holds a Bachelor of Arts in English from University of Washington and attended the professional SF/F workshop Viable Paradise.

Does Using Grey Water to Water One’s Plants Affect Their Growth?

Introduction: Does Using Grey Water to Water One’s Plants Affect Their Growth?

Scientific explanation of grey water's affects on plant growth. Quick and easy to follow.

Step 1: Background Information:

Today we are faced with two significant issues in society: the overuse of the finite supply of water in the world and the cost of living. Many households save both water and money by recycling grey water on their garden. This means watering ones garden with old dishwashing water, shower water or laundry water. However, does the soapy water negatively affect the plant’s growth and development. Some sources say that “plants have been scientifically proven to grow better with grey water” [1] . However some other sources suggest that it could harm the plant and that normal clean water should also be used. “the potential harm is less to the plants than to the soil, with its complex bacterial and fungal make-up. Recycled soapy water (‘grey’ water) is perfectly usable for plants, but I would not use it exclusively. Rotate it with ‘clean’ water on an alternate basis and, as with all watering, direct it at the roots rather than the foliage.” [2] [1] http://waterwisesystems.com/learn-more/why-a-grey... [2] http://www.dailymail.co.uk/home/gardening/article...

Step 2: Aim

To find out whether using a solution of detergent and water to water plants will negatively effect the growth of that plant.

Step 3: Hypothesis

The more detergent used whilst watering the beans, the less these beans will grow. All the beans will show some growth.

Step 4: Equipment

- 9 Sauces - 18 Lima Beans - 72 cotton wool disks - 20mL Syringe - Cold Water - Washing Detergent - Ruler

Step 5: Method

1. Place all 9 saucers next to each other near a window (ensuring they will receive the same amount of sunlight) 2. Layer 4 disks of cotton wool on each saucer. 3. On each saucer, place 2 beans on the first layer of cotton wool approximately 3 cm apart. 4. Place another 4 disks of cotton wool to create a second layer of cotton wool on top of the beans. 5. Clearly label each saucer so that the concentration of detergent they will be watered with is easy to identify. There should be 3 saucers labelled 10mL, 3 saucers labelled 5mL and 3 saucers 0mL. 6. Immediately water the beans on the 3 saucers, labelled 10mL, with 20mL of water, and 10 mL of washing detergent measured with a syringe. When measuring with the syringe ensure that you are at eye level and measuring to the bottom of the meniscus. 7. Immediately water the other 3 saucers, labelled 5mL, with 20 mL of water and 5 mL of washing detergent measured with a syringe. 8. Immediately water the last 3 saucers, labelled 0mL, with 20 mL of water, measured with a syringe. These are the control. 9. Observe results daily. And when possible record length of beans. 10. Record all results

Step 6: Variables

Variables that need to be controlled and how I controlled them. - Amount of sun/shade, I have placed all the saucers in the same area of the same room for the same amount of time. This ensures that all of the beans receive the same amount of sunlight as well as all the beans are grown in the same room temperature. - Amount of water, Each beans on the saucers will receive 20mL of water daily with an additional 0, 5 or 10mL of detergent daily, this will be measured with a 20mL syringe. - Amount and uniformity of cotton wool, I deliberately used cotton wool discs instead of cotton wool balls as they are all the same. I will use 8 discs of cotton wool per saucer. All the cotton wool is the same brand and from the same box. - No air in syringe, before drawing up the liquid, I pushed the syringe all the way down as well as I held it underwater to let all the air escape. This ensures that the amount of liquid that the syringe says is drawn up is that same amount as the liquid in the syringe.

Step 7: Observations

The cotton wool absorbed water incredibly quickly, and after my first day I had decided to double the amount of water, and concentration of detergent to make sure the cotton wool was soaked. After 2 days the colour of the cotton wool on the saucers labelled 5mL and 10mL started to go yellow. The colour of the cotton wool with 10mL of detergent was undoubtedly stronger than the colour on the cotton wool with 5mL of detergent. My control beans grew much faster and stronger than the beans watered with 5mL of detergent. The beans watered with 10mL of detergent did not grow at all. At the end of the experiment the beans on the saucer labelled 5mL grew small white stems, just like my control bean had done after 1 or 2 days. I also observed that the beans watered with 5mL of detergent grew mould, whilst the others did not.

Step 8: Results

I used the above image as guidelines towards the growth of my plant. Control (0mL of detergent) : Stage at beginning of experiment = 0 Stage after 5 days of experiment = 2 Stage after 11 days of experiment = 4 5 mL of detergent : Stage at beginning of experiment = 0 Stage after 5 days of experiment = 0-1 Stage after 11 days of experiment = 2 10 mL of detergent : Stage at beginning of experiment = 0 Stage after 5 days of experiment = 0 Stage after 11 days of experiment = 0 Image without stage labels found at http://www.buzzle.com/articles/life-cycle-of-bean...

Step 9: Further Results

Step 10: Total Length From the Roots to the Leaves of the Beans at Conclusion of the Experiment

A) Total lengths of Lima beans watered with 20mL water were, 9cm, 2cm, 3cm, 7.5cm, 3.5cm and 8.5cm. Therefore the average length for the control beans was 5.6 cm. B) Total lengths of Lima beans watered with 20 mL water and 5 mL liquid soap were 1.5cm, 0.5cm, 0cm, 1cm, 0cm and 0cm. Therefore the average length of Lima beans with 5mL added liquid soap was 0.5cm. C) Total lengths of Lima beans watered with 20mL water and 10mL liquid soap were 0cm, 0cm, 0cm, 0cm, 0cm and 0cm Therefore the average length was 0cm.

Step 11: Conclusion

I successfully followed my method but discovered that my hypothesis was only partially correct as I stated that all the beans would grow. Even the slightest measurement of washing detergent will negatively affect the growth of the plant. Once the concentration reaches 1/3 detergent the beans will no longer grow.

Step 12: Discussion

During my experiment I have found out that the more soap in the water the less absorbent the cotton wool was. This could have altered the results as the cotton wool was not absorbing as much water and therefore the bean was not receiving as many nutrients. If I were to redo the experiment perhaps I could put fresh cotton wool discs daily. I also discovered that the beans watered with 5mL added detergent started growing a mould like substance although the beans watered with 10 mL added detergent did not. I do not know why it was only on the 5mL detergent saucers that grew anything whilst the other two remained clear. Further experiments may answer this. This is also interesting because the detergent is anti-bacterial and I thought that this would prevent the mould like substance growing. This is shown on the 10ml added detergent beans. Even though I tried to control the amount of sunlight as my variables by placing all the beans in the same area, I did not think about the distance from the window would make such a difference. The beans furthest away from the window grew the largest while the beans in between the window and furthest away from the window grew the shortest. I think this is because the beans received too much sunlight. However this did not affect the results of my experiment as I had three versions of each concentration of detergent. Layout closest to furthest from the window, so that when I take an average they all get the same amount of sunlight.

Step 13: Bibliography

All your plants, even your natives, love greywater. Available: http://waterwisesystems.com/learn-more/why-a-grey-water-garden/all-your-plants-even-your-natives-love-greywater. Last accessed 5th Mar 2014. Don M. (2010). Is it Wrong to Hydrate my Plants with Soapy Water .Available: http://www.dailymail.co.uk/home/gardening/article-1296007/ASK-MONTY--Is-wrong-hydrate-plants-soapy-water.html. Last accessed 5th Mar 2014. Elaine p. (). Information About Beans in Cotton Balls. Available: http://www.ehow.com/info_8130551_information-beans-cotton-balls.html. Last accessed 5th Mar 2014. Scholasticus K. (8/13/2012). Life Cycle of a Bean Plant. Available: http://www.buzzle.com/articles/life-cycle-of-bean-plant.html. Last accessed 5th Mar 2014. Williams J. (). How to Grow Bean Seed in Cotton & Water. Available: http://www.ehow.com/how_6005412_grow-bean-seed-cotton-water.html. Last accessed 5th March 2014.

• For Teachers

• Everyday Activities
• Experiments

Can you "water" plants with other liquids?

• Challenging
• A Bit Messy
• 15 Minutes each day; 1-2 weeks

Water seeds with other liquids and see if they grow.

Most seeds need warmth, light, and water to start growing. But what happens when you replace water with other types of liquids? Test them out using this experiment!

You Will Need

Four plastic cups

Water, and three other liquids. Choose any liquids you want, but some suggestions are saltwater, sugar water, vinegar, soda, juice, or even dish soap!

Seeds - enough for 3 for each cup, any kind you want to try to grow. Examples of fast-growing seeds are marigolds, sunflowers, beans, and peas.

4 labels (one for each cup)

Liquid measuring cup

Paper (to document your experiment and your findings)

Note: For any experiment, it is important to control the environment so there is only one variable (or one thing changing, which in this case is the liquid you are using). Make sure the seeds are all the same variety, that the cups are set up exactly the same way, and the cups are kept in the same area while you wait for the plants to grow.

• Ask your scientist to pick 3 different liquids.
• On the sheet of paper, write down which liquids you have decided to use.
• Ask your young scientist to make predictions. What do they think is going to happen with each seed? Which will grow the fastest? Which will grow the slowest? Which will not grow at all?
• Gather the water and your three other liquids. If you are mixing liquids, write down the measurements you use so they can be made the same way each day. (For example, if you mix 1 teaspoon of salt into 1 cup of water for saltwater, repeat that same ratio the next time you water your plants.)
• Label each cup with the name of the liquid you are planning to use.
• Fill each cup about ⅓ full with dirt.
• Add 3 seeds to each cup and cover with a little dirt. Make sure to not plant the seeds too deep into the soil or they might not get enough light to grow.
• Place the cups in a sunny, warm spot.
• Decide on the amount of liquid you will use to water each plant. We recommend 2 to 4 tablespoons of liquid in each cup, making sure not to drown the seeds in too much liquid.
• Using the labels on each cup as a guide, encourage your young scientist to measure the liquid needed, and pour it into the corresponding cup.
• Over the next several days, keep adding the designated liquid to each cup, being sure to keep adding the same amount. Only add when the soil is dry to avoid overwatering the plants.
• Encourage your scientist to make observations each day, and note them on the piece of paper. What do they see? What’s happening with the seed using plain water? How does it compare with the other seeds?

Experiment Extensions

• Try this experiment using other variables. For example, water all the plants with plain water, but try varying the amount of light they get. Or try growing one plant in a warm spot and another in a cold spot. Try it and see what happens!

How it works

Plants have been growing for millions of years, making their own food from water, carbon dioxide, and light. When you try to grow plants using another liquid, the molecules (or what makes up that liquid) are shaped differently from water molecules. Because of their different shape, they block the process of photosynthesis from occurring, so the seeds do not know they should grow!

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Paper Towel Science Experiment

Does your paper towel absorb more water? Let’s test it! This fun paper towel science experiment will help determine which brand absorbs the most water. It is a hands-on science fair project idea that teaches the scientific method in action, perfect for elementary students learning about materials and their properties.

Paper Towel Science Fair Project

In this science fair project, you’ll investigate how different brands of paper towels absorb water. You’ll compare multiple brands and use a simple measurement process to see which towel holds the most water. This is an excellent opportunity to explore the science behind materials and use the scientific method . Plus, it’s easy to do at home or in the classroom!

💡What is the most absorbent paper towel brand? Is it Bounty or Sparkle or another one?

Grade Level Recommendation:  3rd to 5th grade

• 3 to 5 different different types of paper towels
• Measuring cup or clear plastic cup
• Small bowl of water
• Paper and pen for recording data
• Printable chart for tracking results (free download below)

Paper Towel Science Experiment Instructions

Step 1:  Take one sheet from each roll of paper towels (make sure they are all the same size).

Step 2:  Fold the first towel into a square.

Step 3:  Drop the towel into a small bowl of water.

Step 4:  Once saturated, hold it above the bowl until it stops dripping.

Step 5:  Squeeze the towel over a measuring cup or clear plastic cup to measure the amount of water absorbed.

Step 6:  Mark the water level and label it with the brand name. Repeat this process for each towel brand.

Step 7:  Record the amount of water absorbed by each brand and rank them on your printable chart.

Paper Towel Science

The absorbency of a paper towel is determined by its fibers and structure, which create small spaces that water can fill. This process relies on two forces: adhesion (water molecules sticking to the fibers) and cohesion (water molecules sticking to each other). As the water fills these spaces, it gets trapped, allowing the towel to absorb liquid.

This process is driven by capillary action —the movement of liquid through small spaces. Towels with more fibers or layers have a greater surface area, allowing them to absorb more water.

Thicker paper towels or those with multiple layers (like quilted patterns) generally absorb more water because they have more fibers and space to hold liquid. Some brands also add treatments to increase absorbency. This experiment helps explore how materials are designed for different purposes.

You may also notice that price doesn’t always reflect performance. Some more expensive towels may include treatments that reduce absorbency but increase wet strength, highlighting the balance between absorbency and strength in products.

💡 In this  paper towel absorbency experiment , here are the key variables :

• Dependent Variable (What you measure): The amount of water each paper towel absorbs (measured in ounces or milliliters).
• Independent Variable (What you change): The brand of paper towel used in the experiment (you are testing different brands to see how they perform).
• The size of each paper towel sheet (make sure all sheets are the same size).
• The amount of water in the bowl.
• The method of folding and immersing the paper towels.
• The temperature of the water.
• The time allowed for the paper towel to drip before squeezing.

Using the Scientific Method

💡 Learn how to apply the scientific method to your experiments for a complete science fair project .

Ask a Question:  Which brand of paper towel absorbs the most water?

Do Background Research:  Look into how paper towels are made and what makes them absorb water. Research different brands—do some advertise being more absorbent?

Form a Hypothesis:  Make a prediction based on your research. For example, you might predict that the thicker, quilted paper towel will absorb the most water.

Test the Hypothesis (Experiment):  Follow the steps to test each brand and measure the amount of water absorbed.

Analyze the Data:  Use the measurements from your chart to compare results. Rank the brands based on how much water they absorbed.

Draw a Conclusion:  Determine which brand absorbed the most water. Was your hypothesis correct?

Extension Activities:

Strength Test:  After the absorbency test, test the strength of the paper towels when wet by adding small weights such as pennies until they tear. Which brand holds up the best?

Environmental Impact:  Research how paper towels are made, including whether they are biodegradable or made from recycled materials. Compare eco-friendly brands and their absorbency.

Cost Comparison:  Look up the price of each brand tested and compare the cost to its performance. Is the most absorbent towel the most expensive?

Absorbency with Different Liquids:  Try using liquids other than water, such as soapy water, to test whether paper towels absorb them differently.

Related Science Activities

• Capillary Action in Plants :  Place celery or white flowers in colored water and observe how the liquid travels up the stem. This demonstrates plant capillary action , similar to how paper towels absorb water.
• Walking Water Experiment : Similar to plant capillary action, this experiment uses paper towels to demonstrate the process.
• Material Properties Test :  Test the absorbency of other materials, such as cotton, sponges, or even tissue paper, and compare their effectiveness to paper towels.
• Evaporation Exploration:   Leave the soaked towels out and record how long it takes for each brand to dry completely. Which brand dries faster, and why?
• What Absorbs? : Learn more about how different materials absorb water or do not.
• Natural vs Man-made Materials : Explore natural and manmade materials.

More Science Experiments for Kids

Helpful Science Resources

Here are a few resources that will help you introduce science more effectively to your kids or students and feel confident presenting materials. You’ll find helpful free printables throughout.

• Best Science Practices (as it relates to the scientific method)
• Science Vocabulary
• All About Scientists
• Free Science Worksheets
• DIY Science Kits
• Science Tools for Kids
• Scientific Method for Kids
• Citizen Science Guide
• Join us in the Club
• Printable Science Project Pack

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• Home Improvement

Will Soapy Water Kill Plants?

Gardeners have doused plants with soapy water to kill insects for at least 200 years. But that doesn't necessarily mean it's a good idea. For starters, "soap" can mean a lot of different things, and the soap products available today can vary dramatically from those sold 50 or 100 years ago. So the question remains: Will soapy water kill plants? The answer is yes, if it's the wrong kind of soap or if it's the right soap and it's used improperly or on the wrong type of plant.

Soaps used for insect control on plants range from general-purpose detergents to commercial insecticidal soaps formulated specifically for plant application. Any soap solution can harm plants if not used correctly, and many homemade solutions involving household soaps and detergents can harm plants with any application. For this reason, it's important to avoid any soap product that is not specifically labeled for use on plants. It's also worth nothing that some horticultural experts advise against spraying plants with soapy water of any kind.

Here are some things to consider before you attempt to use soapy water to remove pests from your indoor or outdoor plants.

How Soapy Water Kills Insects

Soapy water can be an effective insecticide for common soft-bodied pests like spider mites , aphids, whiteflies, soft scales, psyllids, earwigs, mealybugs, and thrips. Hard-shelled or larger insects, such as many beetles and caterpillars , aren't usually affected by insecticidal soaps.

Though the precise mechanism isn't certain, experts believe that soap kills insects by disrupting cell membranes or possibly removing their protective wax coatings, causing their bodies to dry out. Soapy water kills insects only when it is sprayed directly onto their bodies; it is not effective to spray plants when no insects are present. Soapy water often must be applied repeatedly, and it washes off with rain, requiring reapplication.

Commercial insecticidal soap is the safest choice because it's formulated to control pests and minimize injury to plants when used as directed. These products are considered an organic pesticide, which is not true of most common household soaps and detergents. Any soap at high concentrations can burn plant foliage, especially when applied on hot, humid days when the temperature exceeds 90 degrees Fahrenheit.

Some soap products are particularly harmful to plants. Detergents used in dishwashers and clothes washers can be especially harsh. These detergents may contain chemicals like bleach, which will damage leaves, and boron, which can build up to toxic levels in the soil. Some dishwasher detergents also contain water-softening salts that are harmful to plants.

Even liquid dish soaps, like Dawn, Joy, and Palmolive, have grease-cutting power that can strip the waxy cuticle from leaves, drying out the foliage and making the plant more susceptible to disease. Hand soaps and detergents may contain antimicrobials that will kill beneficial microorganisms in the environment.

Plants That Burn From Soapy Water

Some plants are too delicate even for specially formulated commercial insecticidal soaps. These include sweet peas, some varieties of tomatoes, hawthorns, portulaca, bleeding hearts, and ferns as well as some flowering fruit trees, such as plum and cherry. Do not use any type of soapy water or insecticidal soap on these plants. If you buy insecticidal soap, check the label to see which plants are especially sensitive to that product.

Safely Using Soapy Water

Some general-purpose soaps are labeled for use as insecticide on plants. One example is Dr. Bronner's Pure-Castile Soap . According to its label, this soap should be mixed with water in a ratio of 1 tablespoon of soap liquid per quart (32 ounces) of water to make an insecticidal spray. Here are some tips for using this or any other soapy water solution on plants:

• Use filtered or distilled water for making the solution if your home has very hard water. Over time, hard water can lead to a buildup of minerals on plants.
• Choose unscented soap if you're concerned about soap fragrance or additives affecting the flavor of edible plants.
• Don't spray wilting or drought-stressed plants under any circumstances.
• Apply the spray in the morning or evening when your plants aren't in direct sun.
• Spray the soapy mixture directly on soft-bodied insects, limiting unnecessary spraying of leaves and avoiding tender young foliage. Check the undersides of leaves, where insects often congregate, and spray any you find.
• Rinse off the plants a couple of hours after spraying, if desired, to minimize potential damage.
• Repeat application of the spray as directed until the insects are under control.

Other Uses for Soapy Water

While soapy water isn't always the best choice for spraying plants, there are other ways you can use it as an insecticide in the garden. For example, you can use a bucket of soapy water to kill pests that you handpick from your prized roses or precious tomato plants. This method is very effective for larger insects, like Japanese beetles or cabbage worms. The soap breaks the surface tension on the water, causing the insects to sink and drown.

Recommended

June 25, 2015

Measure Surface Tension with a Penny

A soapy science activity from Science Buddies

By Science Buddies

Learn about the secrets of soap in this surprising surface tension-testing activity!

George Retseck

Key concepts Chemistry Molecules Surface tension

Introduction Have you ever noticed on a rainy day how water forms droplets on a window? Why does it do that instead of spreading out evenly over the whole surface? You might not guess it but this property of water is also related to washing dishes and doing the laundry. How? It all has to do with something called surface tension. Try this activity to learn more!

Background You have probably noticed that if you look at a surface outside on a rainy day or spill some water inside, the liquid tends to form droplets that stick up from a surface instead of spreading out into an even sheet. This occurs because water is made up of many tiny molecules that are all attracted to one another. Molecules in the middle of a drop of water are pulled evenly in all directions by all the nearby molecules. Those near the droplet’s surface, however, are pulled mostly inward by the water molecules below them. This creates "surface tension." The surface of the water droplet is held together by the attraction between molecules.

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Now, think about washing dirty dishes or clothing. There will be lots of tiny little holes and cracks that water needs to get into to wash away dirt and grime, such as the spaces between the fibers of a shirt or between a plate and bits of dried food. In order for water to flow more easily into these small spaces, you need to decrease its surface tension. You can do this by adding soap, which is a surfactant (a material that decreases the surface tension of a liquid). In this activity you will see how soap decreases the surface tension of water by putting water droplets on top of a penny.

Medicine dropper or eyedropper

Glass, cup or small bowl

Dish towel or paper towel

Flat, level surface that can get wet, such as a kitchen counter

Paper and pencil or pen (optional)

Preparation

Place your penny on a flat, level surface that can get a little wet, such as a kitchen counter.

Fill a glass, cup or small bowl with tap water.

Fill the medicine dropper with water.

Now carefully add one drop of water at a time to the top of the penny. Hold the medicine dropper just above the top of the penny (not touching it) so each new drop has to fall a short distance before it merges with the drop on the penny. You can write down the number of drops you add if you like. How many drops of water do you think will fit on top of the penny? Watch the drop on top of the penny carefully as it grows. It should keep getting bigger and bigger until it touches the edges of the penny.

Keep adding drops (refill your medicine dropper as necessary) one at a time. How big does the drop on the penny get before it finally spills over the edges?

Once the drop spills over the penny’s edge, use a towel to completely dry off the penny and surrounding surface. How many drops of water were you able to add before the water ran over the penny’s sides?

Mix a small amount of dish soap with your tap water.

Now, repeat the experiment using soapy water. Do you think you will be able to add more drops or less before the liquid spills over the sides of the penny? Again, slowly add one drop at a time. How big does the drop of water on top of the penny get before it breaks and flows over the edges?

Extra : Try the experiment with different liquids or other things you can find in your kitchen. (Make sure you have an adult's approval to use any liquids before you handle them.) How do different soaps and detergents like hand soap or laundry detergent compare with one another? What about other liquids like milk or juice? Which ones make the biggest (or smallest) drops? With the most or least number of drops?

Extra : Try using something other than a penny to collect the droplets. What happens if you use different materials, such as the flat top of a small plastic bottle cap or a button?

[break] Observations and results You should find that plain tap water produces a much larger, stable drop of water on top of the penny than the soapy water does. This is because plain tap water has higher surface tension, so the surface is "stronger" and can hold together a larger drop. Adding soap lowers the water’s surface tension so the drop becomes weaker and breaks apart sooner. Making water molecules stick together less is what helps soaps clean dishes and clothes more easily.

More to explore Sticky Water , from Exploratorium Soap , from Exploratorium Measuring Surface Tension of Water with a Penny , from Science Buddies Surface Tension Science: Build a Raft Powered by Soap , from Scientific American Science Activities for All Ages! , from Science Buddies

This activity brought to you in partnership with Science Buddies