Diatomaceous Earth

Last year I had a terrible time dealing with fungus gnats and aphids on my seedlings. As I have no greenhouse or indoor setup, I rely on taking the plants out during the day and in at night. Luckily I’m in a climate that lets me do that in the winter. The seedlings get a great start this way, with strong sun and good breezes that make the little plants strong, but it also exposes the delicate seedlings to a myriad of nasties.

This year has been great so far. I now cover the seedling trays with shade cloth when I take them outside. The holes are small enough to keep the wildlife out and still allow sun and wind to get to the plants. So far, I haven’t had one aphid on the plants and only one fungus gnat snuck in.

I was wondering if anyone has tried diatomaceous earth to combat fungus gnats. I would think it should work well.


I’ve had serious infestations of fungus gnats quite a few times over the years. Just recently I came across a suggestion to use “mosquito dunks” in a jug of water, and then water with it. It makes sense, since “mosquito dunks” are those little doughnut shaped floating things that slowly release a strain of bacteria (Bacillus thuringiensis israelensis) that affects mosquito and blackfly larvae. It seems that fungus gnats are susceptible to this bacteria as well; it’s the same strain used in “Gnatrol”, sold for fungus gnat control. I’ve just started using it myself so I can’t comment on its effectiveness yet.

As far as diatomaceous earth goes, I can’t see where it would hurt to try it. I’ve also read somewhere that a layer of sand at the surface can help with fungus gnats.

Good luck, Tom

Thanks, Tom. I did hear from someone who used DE lastyear and she said it worked very well. As you say, can’t hurt. I looked into Gnatrol and it does look good. Since I grow my seedlings in the house I need to be careful, but Gnatrol is Bacillus thuringiensis which should be ok for indoors. I’ll check into it further.

I was one who used mosquito dunks and it didn’t work at all well for me. They don’t disolve well in the water and whatever the meduim is gets all yucky in the pot.

I now use a hanging “pest strip” called “Revenge”. It is indicated for use in dog runs, kennels, dairy rooms, etc and is only contraindicated for use in food prep areas.

It has been 100% effective for me and I used to be plagued with those little bugger fungus gnats until I started using them. I found mine at Fred Meyer in the garden center, and at a local feed store.


Good idea! Glad to hear that works well.