I tend to always have a few around, here and there, but nowhere near as bad as when I first started collecting plants again (about two years ago), and I have several times more plants now than I did then. Like, 383 plants now and 15 plants then. It's usually a sign that the plants are overpotted (in pots too large for the root ball) or overwatered (being kept consistently too wet).[1] Better watering will take care of most of the problem without having to try anything more strenuous. In previous fungus gnat threads on Garden Web, people have advised pouring bleach down drains, because they will lay eggs down there occasionally; that could maybe be enough to sustain a population, though I'd be surprised. I'm also told that spreading a layer of sand on top of the soil will cut way back on them (adults can't get through the sand to lay eggs; larvae can't get through the sand upon adulthood). And there are sprays and stuff for them, though I really have a hard time imagining that sprays would actually be necessary for most people. I'm a little curious about how many plants, and how many gnats, we're talking about: what you consider a lot and what I consider a lot may not be the same thing. [1] I mean no disrespect by asking, but -- when you say you don't overwater, how do you know you're not overwatering? What happens when you water less often? Pothos in particular is easy to overdo.

You've got to kill the larvae. Use Mosquito Bits and/or Mosquito Dunks. I buy the Bits on Amazon; it's $10, and you can treat 20 or so plants for a couple of months with it. With the Bits, you shake a good amount over the top of the soil, and whenever you water, the bacteria will wash down into the soil ... kills the gnat larvae, not the plant. The dunks go in the watering container. What will also help immensely is to allow the plant to stay as dry as possible, even to the point of stressing the plants. Larvae can't live in dry soil. Most of my plants are succulents and can take a little drought, but I have a few that need moisture at all times or the leaves will start dying. I refresh the Bits on those plants once a week. Eventually, the gnats will be gone. It will take 2-3 weeks of vigilant treatment every time you water. Good luck. I HATE FUNGUS GNATS!

I"m sure there's a lot of smart people here that know a lot more about plants and house plants than I do but to say that "If you have gnats, there's a 99% chance your plants are suffering from excess water retention", just isn't true. I've had the same 28 house plants for 5-15 years (depending on the plant) and all are thriving. I've only had a Dracaena die on me a few years ago due to my water quality i believe but it certainly wasn't root rot. Last July, a friend of mine gave me this amazing Philodendron Micans becuase he was leaving the country. Shortly after getting the plant, my wife and I went away for 10 days. We came back to fungus gnats. I immediatley quarantined the new Micans and completely changed the soil but it was too late. Many of my other plants, including plants i run very dry like ZZ, hoya, snake plant had fungus gnats. I've never had a fungus gnat issue in the past so i really didn't now what to do. Like many people, I tried using BT and yellow sticky tape combo (the rememdy that many poeple are recommending), Bonide systemic granules, hydrogen peroxide, diatamacious earth, neem oil and nothing worked. I tried completely drying out my soil and again, fungus gnats came back weeks later. After hours of gnat research, I read about someone with a similar problem and she said to cover the drainange holes in all your plants and cover the top layer of soil with sand. It appears that fungus gnats are skilled at finding any moist soil, top or bottom so they can and will use your drainage holes to lay their eggs. Their eggs can also lay dormant for many weeks in dry soil and then hatch again when you water your plant so drying out your soil, even the top two inches bone dry, doesn't always work. So no, it doesn't take just poorly drained plants to make fungus gnats happy. Poorly drained soil certainly helps them thrive but they will thrive just fine even in slighly damp, properly draining soil. I was desperate and I really hated covering my soil with sand and wil likely remove it at some point but i'm happy to report, i've been fungus gnat free for about 2.5 months and all plants are doing fine. You have to make it impossible for any gnat to gain access or escape from your plant's soil. This will break the life cycle. Hopefully this is helpful to anyone else looking for a gnat solution. (And there's no sign that my plants are under any additional stress due to the sand compacting the soil undernearth. I used about 1/4 - 1/2 inch of sand, just don't go too crazy with the sand and you will also have to slow down your watering because the water pools temporarily on the top of the sand before it is absorbed and reaches the soil underneath)

Hi, thank you for that! Here's a follow up, as I think it would be helpful for anyone who has similar situation to me. I prepped the H2O2 per your suggestions shortly after posting, then left for a week long conference. I had intended to run the tests after returning. Interesting development, however: when I got home, the gnats were gone! I think what happened: the weather forecast correctly predicted a dry heat wave, so I setup a string wick to water the plants while I was gone. When I returned, I noticed the soil was very dry in the top-two inches. It's likely these conditions prevented further egg laying, as they have not returned in 30 days. Woohoo! Further research has taught me that self-watering based containers can also help control fungus gnats since top portion of the soil can dry out, which discourages the buggers from laying their eggs -- all depends on the setup, of course. Well, I'm happy :)