How to Use Kaolin Clay to Battle Japanese and Cucumber Beetles, Grasshoppers and More

Kaolin clay is a mineral used in toothpaste, cosmetics, medicine and a variety of other products. Fruit orchards have used this product to prevent insect damage and sun scald, but it has not been well-marketed to the home gardener.

I consider it a staple in my garden, and the organic gardener's best-kept secret. It doesn't hurt or kill beneficial insects, but it coats plants with a sticky barrier that repels and confuses them. I have used it successfully for three years against a gardener's worst enemies: Japanese beetles, cucumber beetles (my worst foe) and more. Research has shown that kaolin clay is an effective repellent for over 100 types of insects.

Kaolin clay for horticulture is marketed under the brand name Surround WP and typically comes in 25-pound bags. This is much more than a gardener needs, but there are a few places online that sell it in smaller bags. I have a five-pound bag that has lasted three years, and will probably last another two or three years.

Difficulty: Moderate

Instructions

Things You'll Need:

• Kaolin Clay
• Garden Sprayer
• Water
• Stick for stirring

1. Read the mixing instructions carefully. The ratio of clay to water will depend on its use.

2. Per the instructions from the manufacturer, fill sprayer half full of water and while stirring, slowly add the kaolin clay.

3. Shake the closed container vigorously for 30 seconds.

4. Add remainder of water and shake for an additional 30 seconds. Shake the sprayer occasionally during application.

5. 
   Spray kaolin clay onto plants

   Spray on plants and seedlings using your sprayer. You should thoroughly coat the leaves and stems of the plants, including the underside of the leaves. Any parts of the plants that need protection from insects need to be coated, including fruits.

6. 
   Cover all parts of the plant, including stems

   Apply it thickly enough that it nearly begins to drip off the leaves (but not so it actually runs off, which wastes product).

7. 
   Lush green turns dull with a whitish film

   Wait an hour or so and check your results - your plants should clearly show a grayish film. For full protection, a second coat should be applied.

8. Reapply when the film wears off, or is washed off by rain.

9. Rinse your sprayer and store for next application. Do not store extra solution in the sprayer.

Tips & Warnings

• The earlier in the season you begin kaolin clay application, the better. The clay is thought to work in a couple of ways, including confusing insects and sending them elsewhere. But it can be used at any time.
• The manufacturer and researchers say that kaolin clay will not harm pollinators such as bees. However, because pollination is crucial to setting most fruits, I do not coat flowers. The exception is my cucumbers because cucumber beetles love those. This means I do some hand pollinating just in case.
• Invest in a real sprayer - a hand squirter will wear you out.
• Apply only to dry foliage, and on a day when rain is not expected.
• I use two coats for full protection.
• Reapply about once a week unless you have heavy rain, and then reapply after the foliage dries.
• I make sure my squash stems are heavily coated to repel squash vine borers, another pest that bothers my garden.
• The clay needs time to dry, but if it hasn't dried to a nice white/gray color after an hour, give it another coat.
• Kaolin clay may be applied up to the day of harvest. Rinsing the fruit is recommended.
• Kaolin clay can also help with sunburn and heat stress on plants and fruits.
• Surround WP is OMRI listed.
• Do not store leftover product in the sprayer.
• Dispose of excess product in accordance with applicable laws and per the manufacturer's instructions.
• If you accidentally spray it in your eyes, flush with water and call a physician if irritation persists.
• Wash hands after handling.

Resources

• Cornell Resource Guide - Kaolin Clay