Diatomaceous Earth – Razor Wire for Your Garden

Lately my compost has been overrun with fruit flies. I have a tumble composter, so I suspect that it will eventually reach a point where it is hot composting (perhaps after the nights stop being so cold) and that will probably burn them off. But in the meantime, it is pretty uncomfortable to even look in there. You get a face full of fruit flies for your trouble. I tried beneficial nematodes, but it’s been almost a month since application and the flies are still a problem. I have thought about spraying neem oil or some other pesticide, but that bothers me from two different angles. The first is that I don’t really like the idea of putting pesticide in my compost, even if the pesticide is organic. The second is that it would kill the adults while it is the larvae that really need killing, so new applications would be needed every few days to have any effect. I also tried sealing up the compost and letting the lack of oxygen kill the fruit flies, but there are too many holes and hinges and such to get a good seal. So I decided to go with physical controls.

A diatom is a type of single-celled algae that is common in all the oceans and has been for millions of years. Diatoms have a unique cell wall that is composed of silica. Interestingly, each species of diatom has unique physiology and can be identified by the shape of the silica “shells” called frustules they leave behind. This knowledge is often used as an easy way to identify the approximate age of marine sediments.

In some areas there are sediments that are composted almost entirely of diatoms, called diatomaceous earth. These sediments are easily crumbled into a fine white powder and sold at garden centers everywhere. When diatomaceous earth is applied to the garden, those microscopic spikes form a sort of razor wire over your soil. When insects walk over them, they produce tiny cuts in the insect’s exoskeleton, which allows the insect’s bodily fluids to leak out, leading to dehydration and death. When applied to compost, it should kill the fruit fly larvae and might kill adults as well. When applied to the garden, it will kill a number of different pest species, especially ones who drag their bellies on the ground. Eventually, the silica breaks down and is incorporated into the soil. It is worth mentioning that it doesn’t seem to have any deleterious effect on humans or larger animals, including earthworms, as our skin is too thick to be cut by the tiny spines. I have also heard that they make a medical grade diatomaceous earth that you can swallow to kill intestinal parasites.