How to Use Diatomaceous Earth as an Organic Pesticide in Your Garden

Diatomaceous Earth, derived from the fossilized remains of Diatoms, is an effective organic pesticide for many garden pests. Unlike chemical pesticides, it poses no risk for kids, pets, wildlife or you.

It’s a beautiful spring morning. You go outside for your daily stroll around your garden and you stop short when you pass the hostas. Was someone using them for target practice last night? The foliage was beautiful yesterday and this morning it’s riddled with holes inside and at the edges. In less than twenty-four hours your hosta has gone from showcase quality to in-need-of-emergency-care

When plants develop damage like this seemingly overnight, the culprit is usually slugs or snails, which are also known to snip off tender shoots, including flowers and fruit. This damage creates stress on the plant and when the foliage is full of holes, a reduced ability to perform photosynthesis. The result is reduced growth and conditions favorable for other pests and diseases to attack the plant while it’s in this vulnerable state.

Slugs and snails crawl over your plants at night and cloudy days, chewing their way through your garden. When the sun is shining they hide where it’s cool and damp – usually at the base of the plant near the soil, or on the underside of large leaves. A dead giveaway of their presence is a “slime trail” – a track of mucus running down the leaves, usually on the underside.

In your panic, you might be inclined to grab a bottle of chemical pesticide and obliterate whatever it is that’s eating your plants, but that’s always a bad idea. Chemical pesticides may kill the target pest, but they’re also frequently toxic to birds, fish, and mammals-including you, your family, dogs and cats and other wildlife.

Diatomaceous Earth controls slugs and snails

For slugs and snails there are a number of well-worn remedies which work quite well, such as removing leaf litter from your garden bed (depriving them of any cool, damp hiding place); hand picking; beer traps; and generally making your garden less hospitable to the critters. If those methods fail to reduce or eliminate the damage, then it’s time to use an organic pesticide and one of the most effective is Diatomaceous Earth. DE as it’s known, was used widely for about one hundred years before chemical pesticides were invented. Now that the dangers of chemical pesticides are well documented, DE is once again returning to use in agricultural and gardening circles.

What is Diatomaceous Earth?

Diatomaceous Earth is a 100% organic pesticide, derived from the fossilized remains of Diatoms, a type of hard-shelled algae. Diatoms are phytoplankton used as food by freshwater and marine animals. When they die, their skeletons settle to the ocean or lake floor and over time become thickly fossilized deposits. These are mined and milled and sold as various grades of DE for industrial and agricultural applications.

What garden pests does Diatomaceous Earth control?

According to the University of Arizona’s College of Agriculture And Life Sciences, DE is effective on any pest or insect with an exoskeleton, which includes those with six legs and arthropods with 8 or more legs. That definition includes slugs, snails, aphids, gnats, fleas, flea beetles, cockroaches, cabbage root flies, sawflies, coddling moths, twig borers, thrips, mites, scorpions, earwigs, silverfish, ants, bedbugs, pillbugs, ticks, etc.

How Diatomaceous Earth kills garden pests

Open a bag of DE and you’ll see a light, white powdery substance that looks and feels remarkably like talcum powder. To garden pests however, the tiny particles are razor sharp and will slice their exoskeleton when they climb across it. The lacerating of their shell exposes the creature’s inner soft tissue to air, effectively dehydrating the pest within a day or two (called desiccation). If that creature ingests any DE, it will shred their insides. DE is a real death sentence for them, but it’s absolutely safe for mammals, birds, and fish. In fact, food grade DE (the grade you apply to the garden) is added to grain shipments to keep them free of pest infestation.

Note: The Diatomaceous Earth that’s sold for use in pool filters is not the same grade as the DE sold as an organic pesticide. In fact, the filter-type is poisonous to you and your pets and won’t kill the insects. Only buy DE that is marked for use as a pesticide or food additive.

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How To Use Diatomaceous Earth

Only use DE when dry weather is predicted for 72 hours, accompanied by low humidity. Diatomaceous Earth is about 80% silica, so when it comes in contact with high humidity or water, it adsorbs moisture and loses its effectiveness (although opinions differ on this). To apply, sprinkle it on the undersides and the tops of affected leaves, around the base of the affected plants, and on the ground surrounding them. In a day or two, any further damage to your garden should noticeably cease.

As with any organic or chemical pesticide, DE should only be used when other control methods have failed – it’s the nuclear option. While DE is environmentally safe, it will kill anything with an exoskeleton, including the insects which feed on the target pest (not all insects are bad). When using a broad spectrum pesticide you always run the risk of upsetting the balance of your garden’s ecosystem, so use it sparingly and with care.