Organic Pest Control: Diatomaceous Earth & How to Apply It

Diatomaceous earth is an invaluable tool in an organic gardener’s toolbox. Diatomaceous earth, or DE as it is known, is made of the fossilized remains of tiny water plants called diatoms.

Diatoms are microscopic or near microscopic plants (ranging from two to 500 microns, or up to about ½ mm) similar to algae and found in nearly every habitat that contains water. They have distinctive

transparent cell walls made of silicon dioxide hydrated with a small amount of water (SiO₂ + H₂O). Their shapes resemble intricate snowflakes and are the result of the impervious nature of their silica based structure.

So how do these microscopic creatures benefit gardeners? When diatoms die they leave behind chalky deposits of fossilized skeletons known as diatomite. This material is mined and ground to the consistency of talcum powder. DE is composed of roughly three per cent magnesium, two per cent iron, 19 per cent calcium and 33 per cent silica along with several other beneficial micro elements. This composition is useful for both insect control and as a valuable food source.

The fossilized remains of the diatoms cause no harm to humans but to insects these microscopic remains are razor sharp. To an insect it is like crawling through broken glass. The diatoms pierce the exoskeletons of soft-bodied insects causing them to dehydrate and die. Food-grade diatomaceous earth does not contain toxins or chemicals, but it is an effective pesticide against a wide variety of garden pests including aphids, mites, thrips, ants and squash bugs to name just a few.

There are two methods for applying diatomaceous earth to your garden.

Dry Method of Diatomaceous Earth Application

Fill a garden duster, shaker container or flour sifter with diatomaceous earth. Avoid creating dust by using a small shovel or trowel to scoop the powder to the container. Although diatomaceous earth is non-toxic, you should not breathe in the fine dust. Consider wearing a disposable face mask if you will be working with large quantities of the powder or if you have respiratory issues.

Shake the powder onto the plants you desire to treat. The best time to do this is in early morning or late evening, when the plants are wet with dew. The moisture helps the dust to adhere to the plant. Diatomaceous earth won’t harm insects when it is wet, but it will be effective once it dries. Shake the powder on the vegetables as well as the leaves; the powder can be easily washed off the vegetables prior to consumption.

Apply more diatomaceous earth around the base of the plants and the area surrounding the garden; this will keep many crawling insects from ever reaching your plants.

Wet Method of Diatomaceous Earth Application

• Add 4 tablespoons of diatomaceous earth into a one-gallon container of water with a lid the seals tightly. Screw the lid on and shake vigorously until the DE dissolves into the water.
• Fill a spray bottle or garden pump sprayer with the mixture.
• Spray the plants with a fine mist until they are wet but not dripping. Spray the undersides of leaves too.
• Allow the plants to dry. As the water evaporates the DE is left behind as a protective barrier which adheres to the plant’s leaves and stems.

With both wet and dry applications it is important to remember that diatomaceous earth is only an effective pest control when dry; the powder works as long as it is visible. It may be necessary to reapply DE after it rains.

Also reapply the powder if the wind blows it away. Lastly, do not use a heavy layer of diatomaceous earth on the leaves of your plants. This can block sunlight from reaching the leaves and interfere with photosynthesis; a thin, even layer is all that is needed.