The Q&A Archives: Gnats Around Sterilized Soil

Question: A few days after planting seeds in sterilized soil, I noticed gnats flying around the area. What can I do to get rid of these pests safely without a lot of harmful fumes? I have a chronic lung disease and would prefer not to use any bug sprays if possible.

Answer: It sounds like you have an infestation of fungus gnats and you can stop them by interrupting their breeding cycle. They reproduce in the top layer of damp potting soil, so covering the soil with a thin layer of a fast-drying material such as coarse sand or fine gravel, combined with allowing the soil surface to dry out a bit between waterings, should take care of the problem in a week or two.

Since you won't want your seeds to dry out while you are waiting for them to germinate, you might try enclosing the containers in plastic wrap until the seeds begin to germinate. The plastic will maintain the humidity needed for the seeds (but will exclude the gnats) and in my experience is a very good way to start seeds in any case.

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