Fungus gnats love wet and organic conditions. Is there a possibility that you are keeping your plants too wet? Or is there any standing water - like excess water in saucers? Do you pick up any fallen leaves and other plant debris? What kind of 'potting' medium do you use? Is it hot & humid where they are kept? Is there good air circulation?

Thanks for quick response. I'm in Colorado so it's super dry. I don't have standing water anywhere and I'm crazy about keeping the leaves clean. Perhaps I'm keeping them too wet and should wait a couple of weeks before watering again. Most of my plants get really unhappy if I don't water once a week. I think they dry out faster in this climate. I also keep the fan going at all times and open the door when it's nice out. May not have the best circulation other than that.

What's crazy is that they even made a home in one of my large cacti, which gets water maybe once a month!

All winter I use mosquito dunks in my watering can. When it crumbles away I add another quarter of a dunk, the circular kind. No fungus gnats.

Julie_anne

Even if you water them seldom, very peaty soil could be staying wet. I don't know which plants you have, and what kind of soil you use, and many tropical need more frequent watering. How do you check if they need to be watered or not?

Try checking deep in the container few days after watering. Use a bamboo skewer or chopstick, or sharpened wood dowel. Even pencil will do. Stick it at least 3/4 deep, trying to avoid roots. Leave for few minutes, then pull out. If it is dry and clean, plant may need watering soon. If it comes out damp/cold feeling when you touch top of your hand or a cheek, and may even have some particles sticking to it, there is still lots of moisture there.

Soil is most often the culprit. It should be very well draining, made of few different ingredients. Many bagged soils are not very well draining. Adding coarse perlite or pumice and small bark may help. Make sure there are drainage holes in all containers.

Any succulents (cacti are succulents too) need very good drainage. Many of succulent growers use gritty mix, containing very small amount of small bark and lots of inorganic substraes. Sometimes, these ingredients may not be easily found and ppl use 50/50 mix of Cactus & Succulent soil (or more of perlite; one can use pumice instead if available) and report good results.

It isn't recommended to fight fungus gnats with many different chemicals, as some will not even work. Flies themselves do not live very long (just long enough to lay hundreds of eggs and annoy ppl! :) Their larvae, that is in the soil, needs to be destroyed and treatment repeated about every 5 days or so to eliminate future generations.

Here - pls. click me is excellent thread explaining how water behaves in container soils. Maybe you'll be interested to read it.

They could be in your drains. Fungus gnats will breed in sink and shower drains. Try closing the drains until you need them. Then, when you open up the drain, do any gnats fly out?

Thanks all. I will try these new things. Sounds like I might be over-watering and not creating enough drainage.

Using Mosquito dunks works very well. But in long run, make sure you water when needed and provide good drainage, because they will just appear again if they find what they like.

I have had problems with gnats and when I changed my plant's soil to faster draining it really helped. I still water with water that has the Mosquito bits or dunks in it every so often I had read that some city water can be treated with stuff that can "kill" or somehow change the active BT in the products. So I usually buy cheap distilled water (a gallon is 89 cents) for this. I also read that watering with dilute hydrogen peroxide can kill some of the nematodes. I did this when I had a bad infestation and it seemed to help. But I would say the best thing I did was get my plants into fast draining soil. Good luck, they are very frustrating.