I have a single week-old seedling in this Coast of Maine Bar Harbor blend soil: Bar Harbor Blend Premium Potting Soil I mixed the Maine soil with perlite, plus a small amount of "Wonder Soil" coco coir in the center, for germination. The seed germinated (woo hoo!) but after several days the plant developed fungus gnats. I know it was from the soil because I used the perlite and the coco in my previous grow and didn't have gnats. I'm not over-watering, and the humidity is low where I live (too low, actually). I've never had fungus gnats before, so I read up on them. Following some advice I read here on GC and also the internet, I scraped off the top layer of soil and put a thick layer of perlite on top. I killed most of the adult gnats by hand and with duct tape. That was yesterday, and so far no more gnats. Right now the seedling is in a 4" pot and I'll be transplanting in another week or so into a 3 gallon container. I'm wondering if I should dump the soil and buy new, or if I should get some diatomacious earth and continue using the soil. From what I've read, the gnat cycle goes like this: There are eggs in the soil. When the soil is watered the eggs hatch into larvae. The larvae eat organic material in the soil and morph into gnats. The gnats lay eggs in the soil and the cycle starts anew. I've read that the larvae can eat plant roots. If I continue to use the soil and add a layer of diatomaceous earth on top, the larvae will not be able to develop into gnats. BUT won't they still feed in the soil until they morph and die? Is my plant at risk from the larvae if I treat only the surface with diatomaceous earth? At some point all the eggs in the soil will be gone, and no new eggs will be laid since there will be no adult gnats, but will that first generation of larvae do enough damage to worry about? Should I quit worrying and just buy new soil and hope it doesn't have gnats?