If fungus gnats become a serious problem, that indicates other issues. Namely, your soil is drenched and somewhat anaerobic. Having a few around is no big deal, but as others have pointed out, if the larvae become dense enough in populatipon, they run out of microrhizzae to consume and start eating roots. Bummer. But the fact that this is happening points to other problems, which may persist even after the (current) batch of gnats is knocked down. You MUST have soil that drains easily and does not allow stagnation around the roots. Fungus gnats thrive under those conditions. But those conditions also mess up the transport of nutrients and oxygen into the roost, so the overall problem is compounded. Use the best soil you can find (Foxfarm Ocean Forest may be the best soil I've ever used in terms of drainage and proper water retention) and make sure you water through. Don't allow the holes in the pot bottoms to sit in water. Forgive me if you already know everything I've said, but I deal with fungus gnats in a greenhouse constantly. We use them like the "canary in the coalmine". If we see a lot of them, we know our water/soil situation has a problem.
Chromophore Reviewed by Chromophore on . Ravaged by fungus gnats??? I started noticing gnats a while ago but didn't worry about them too much as it didn't look like they were actually damaging my plants. I was getting a lot of stunted growth but didn't connect the two. After a while the gnats got thicker and my plants started turning yellow, drying up and dying. Long story short, I read up a little on the gnats and went to war with them. First of all I keep two rooms. I've got one room for vegetative growth with a couple of t5s and a flowering room with Rating: 5