Kaolin clay (aka: china clay) is an incredibly useful and versatile soft, white clay. It is used in the manufacture of porcelain and fine china.
The term “kaolin” originates from the Chinese word Kau-ling meaning (“high ridge”) designated for a hill in China where Jesuit missionaries first obtained the earliest pure clay samples about 1700 AD.
It is also essential to manufacturing paint, paper and rubber along with scores of other products.
Additionally, it has many uses in health and personal care applications, and it is an excellent addition to your garden pest control arsenal.
In this article, we share information on using kaolin clay in the garden. Read on to learn more.
Pure Kaolin Clay Provides Natural Pest Control
There are some kaolin products (Surround WP) prepared for garden use that are mixed with pesticides and other undesirable ingredients.
This is not necessary for good pest control using this all-natural mineral, chemically inert clay.
Application of pure kaolin to dust crops of all sorts has been shown to be an effective way to reduce negative environmental impacts, prevent disease and deter many different kinds of insect pests.
It only takes a very light application of the powder to attain excellent results.
The application is easy because the very finely ground clay powder mixes smoothly with water and can be applied as a light foliar spray.
This thin layer of clay powder works to baffle pests in that it blocks the scent of the desired plant and (apparently) alters the taste of it as well.
What Kinds Of Pests Does Kaolin Clay Control?
Although this treatment is not effective on all plants against all with pest problems, it is a fairly broad spectrum.
It works especially well on Brussels sprouts, zucchini, eggplant, squash, and cucumber plants to defend against:
…and similar pests.
Organic Pest Control Of Cucumber Beetles
For more on cucumber beetle control, see our article: How To Control Cucumber Beetles
Studies conducted for the United States Department of Agriculture (USDA) has shown that kaolin clay is also very effective in preventing thrips infestation on small fruit trees.
Specifically, an application of the powder applied at 50% bloom deters thrips and provides a number of other horticultural benefits.
Use of kaolin clay at this point in fruit development helps more fruit (such as apple trees and pear trees) to set but does not negatively affect the quality of the fruit.
Furthermore, the application of the clay encourages good growth and does not interfere with the activities of beneficial pollinators.
How To Use Kaolin Clay For Plants
The clay powder should be mixed with water at a rate of three cups of powder per one gallon of water.
Some gardeners like to add a few drops of natural liquid soap to act as a surfactant.
If you are treating mature plants, you can add a little fish emulsion to provide a foliar feeding.
It’s best to put the dry clay into a dry bucket and then gradually stir the water in.
If you dump the water in all at once or try to add the clay to the water (rather than the other way around) you may have trouble with clay sticking to the bucket or lumping up rather than dissolving.
Use an old baking whisk to stir, as this helps prevent lumps.
Even though kaolin clay is an all natural, harmless product, you should use a dust mask and goggles to protect your eyes, mouth, and nose when you handle and mix it.
The powder is non-toxic, and will not seriously harm you, but inhaling it and/or getting it in your eyes would be unpleasant.
How To Apply Kaolin Clay To Plants
As with all foliar sprays, it’s best to apply it on a still day when the sun is not too harsh.
Applying foliar sprays on a windy day results in over-spray and waste of product.
Any time liquid pools on the leaves of a plant, harsh sunlight can become magnified and cause burned spots.
For this reason, it’s best to apply the spray on an overcast morning; however, you should check the weather forecast first.
If it’s about to rain, don’t apply the spray as it will just be wasted.
Once you’ve mixed up your solution, put it in a backpack sprayer for application over large areas, or use a small spray bottle to apply it to just a few plants.
For best results, a sprayer with continuous agitation is recommended.
Alternately, you can use the dunk method demonstrated in the video above.
Regardless of how you apply the solution, you must be sure to coat every bit of the plants’ surfaces.
If you leave any part of the plant exposed, pests are sure to find it.
Every leaf and stem must be coated with a light layer of white clay as a crop protectant.
This will leave your plants looking dusty, but this can be a benefit.
The light dusting of clay particles not only protects your plants against pests, but it also provides some protection from very harsh sunlight.
How Often Should You Apply The Clay?
Generally speaking, you should plan to apply your solution a minimum of twice a month, unless you plan on spending all day handpicking pests.
Remember that you must be vigilant because any leaf exposure opens a window for pests to get in.
You must take care not to wash the mixture off when you water your plants.
Don’t use a sprinkler!
It’s always smarter to water close to the ground because this method results in less water waste and helps prevent problems with fungal infections.
How Does The Clay Deflect Pests?
When pests encounter a plant covered with kaolin clay, they are simply confused. They don’t recognize it as being edible.
This is excellent if you are introducing new plants into an area where pests have been spotted.
Even with an established pest population, you can use the clay to battle the pests and continue adding new plants with some measure of confidence.
Is It Good To Use Kaolin Clay On Tomatoes?
A study conducted in 1985 found that application of kaolin clay to tomato plants grown in very hot, dry conditions in the south-central US improves yield by providing protection from heat stress.
The same study concluded that spraying tomato plants in a non-irrigated field only once with a 5% kaolin and distilled water solution helped the plants retain water and improve yield.
Research conducted in Oklahoma in 2005 and 2006 and published by the American Society for Horticultural Science attempted to replicate the 1985 study.
Researchers wanted to determine how and when kaolin clay (i.e. the product known as Surround WP of which 95% of the active ingredient is Kaolin clay) should be applied to tomatoes being grown for market.
The researchers especially focused on the sun shielding qualities of the product and also wanted to know if Surround WP could prevent the development of beet curly top virus (BCTV) in tomato plants.
BCTV is spread by leafhoppers and has wrought havoc with Oklahoma tomato crops in the past.
Kaolin clay has been used successfully to prevent leafhopper attacks of chile pepper plants in New Mexico.
It stands to reason that it might be an effective insect control against these pests on tomato plants.
The product was mixed with water at a rate of half a pound per gallon of water and applied using a pressurized hand sprayer.
The spraying commenced as soon as the young plants were transplanted to their permanent settings with repeated applications on a regular basis as needed to keep a consistent powdery barrier film on all foliage surfaces.
Spraying was stopped when the plants produced green fruits measuring five centimeters in diameter, or before the first harvest of ripened fruit. The fruit was harvested as needed as it matured.
The 2005 researchers found that the use of kaolin clay actually reduced the amount of fruit produced and the weight of that fruit.
In 2006, they found the kaolin clay had no significant effect on the weight and number of fruit when comparing the output of the kaolin treated plants with the untreated plants in the control group.
Based on these results, the researchers concluded that applying Surround WP which is OMRI certified before the start of harvest does not positively affect yield.
Additionally, they found that a coating of kaolin dust can make it difficult to tell whether the fruit is ready to harvest.
Furthermore, it can be difficult to wash the clay coating off the fruit before sending it to market.
In the course of the study, one plant was found to be affected by BCTV in 2005, and none were affected by this malady in 2006.
It is unclear whether the application of kaolin played a role in this result.
Applying Kaolin Clay Powder to Crop of Tomatoes
Should You Use Kaolin Clay In Your Backyard Vegetable Garden?
Although the use of this natural mineral on tomatoes bound for the market is somewhat uncertain, the bottom line is, you have nothing to lose by giving this time-tested product a try.
Use of kaolin and other types of minerals (e.g. diatomaceous earth) has been a common practice for over 2000 years.
Ancient Egyptian and Chinese farmers made great use of minerals to dust crops, and many kinds of animals instinctively know that taking a dust bath is a good way to repel pests.
This naturally occurring mineral has proven itself generally beneficial for all manner of uses.
Christopher Vincent a researcher at the University of Florida Institute of Food and Agricultural Sciences shares that “kaolin clay outperforms foliar insecticides” for managing spreading psyllids.
Products prepared especially for use in the vegetable are effective against:
- A wide range of insect pests
- Provide a layer of protection against harsh sun
- May even reduce plants’ susceptibility to fungal diseases
One of the best benefits of choosing to use kaolin clay and other natural alternatives is that your:
An added bonus is that you can always tell when it’s time to apply more spray.
When the fine white film:
- Begins to wear off
- Gets washed off by a heavy rain
- Or when new leaves grow
… it’s time to reapply!
Where Can You Get Kaolin Clay?
You can pick up this handy product at almost any farm supply store or yard and garden center. Naturally, you can also order it online at Amazon.