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Diatomaceous earth or DE is safe for use in organic gardens without harming the good guys of the soil food web.

Ask Gardenerd: Roly Poly Problems

Here’s a new question that came in this week:

” I have a ton of roly poly bugs in my raised beds right now… They at the roots/stems of my last round of cucumbers and I would like to get rid of them without hurting my worm population. Can I use Diatomaceous earth? – Tia”

Diatomaceous earth or DE is safe for use in organic gardens without harming the good guys of the soil food web.
Diatomaceous earth or DE is safe for use in organic gardens without harming the good guys of the soil food web.

Hi Tia,

Yes, you can use diatomaceous earth (DE) to get rid of the pill bugs (A.K.A. roly poly) without hurting your worm population. Diatomaceaous earth is fossilized, single-celled organisms from a billion years ago. It pokes holes in insects, leaving them to dessicate and die. Some say instead that DE can absorb copious amounts of moisture and, as hard-bodied insects come in contact with it, it absorbs the waxy protective layer from around the insect. Either way it debilitates the insect to the point that it dies of dehydration.

The thing to know is that DE becomes inert when it gets wet, meaning it looses its effectiveness. Since worms spend most of their time underground where soil is moist, they don’t come in contact with DE applied to the surface of the soil. That said, a worm’s exoskeleton is pretty much impervious to DE anyway. DE works on hard-bodied insects, and worms are soft-bodied. Some say that, much like humans and animals, DE actually benefits the digestive system of worms.

Red Wiggler worms in a worm bin. You can apply Diatomaceous earth to keep fruit flies away without harming worms.
Red Wiggler worms in a worm bin. You can apply Diatomaceous earth to keep fruit flies away without harming worms.

This is a good time to point out that you should be using Food Grade Diatomaceous Earth in your garden. Make sure it says this on the package you buy. There are non-food grade options sold for swimming pools–stay away from these.

Just remember to apply DE when your soil surface is dry and wear a mask to prevent inhalation. Reapply after rainfall or overhead watering. The good news is that DE is effective fairly quickly, so you may only need to do this for a few days before seeing results.

Thanks for writing in about your roly poly problems! We hope this helps resolve the issue. Good luck with your cucumbers.

This Post Has 4 Comments

  1. Tanya

    Will DE work if you bury it underground in the soil to get to unseen grub worms and ant mazes? Thank you

    1. Christy

      Diatomaceous earth becomes inert when it gets wet, so I imagine it won’t do much good burying it. To manage grubs and ants, it’s best to take the biological approach and enhance your Soil Food Web with the proper microbes that go after grubs and ants. There are nematodes available online that can be mixed with water and applied to the soil. They interrupt the life cycle and reduce the population. You may have to apply several times to catch them during different stages of their life cycles. Ants can be managed with Terro baits.

  2. John Manning

    I don’t think that DE should be applied to your worm bin to fight fruit flies. If applied directly to the worms, it will desiccate them. If you wait until all the worms go “underground”, the DE would be applied to a moist surface, which, as you point out, would render it ineffective.

    If a person has a multi-layer worm bin where food is added to the active layer (usually the topmost tray), the person can put a “dummy” tray on top of the active tray and add 2-3 inches of unmoistened shredded paper such as is used for bedding. Fruit flies have a difficult, if not impossible, time getting through this dry bedding. They will be trapped between the active layer and the dummy layer where spiders will eat most of them before the active layer is fed again.

    1. Christy

      The research I did on DE and earthworms shows that their exoskeletons are impervious to DE, but that said, I wouldn’t apply directly to them anyway. We’re talking about putting it in garden soils to deal with other bugs. In this case it won’t harm your earthworms but it will be effective on other critters.

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