Raise the humidity. Fungus gnats, if they are indeed gnats and not whiteflies aphids thrips or spider mites, need humidity.

They lay their eggs in soil. I find a good inch or so of perlite on top as a mulch keeps them from reaching soil.

and by 'raise'i mean 'lower.'

Get Mosquito dunks at the nursery.They are a bacteria that kills a lot of soil born critters.
I float one in a couple quarts of water and water the plants with it.
It killsthe grub stage so you have to water until the flies die and all the eggs hatch and grubs die.
Once you don't see any flies water with it to keep them gone.
They sell it as grauals or donuts.

Shop around for price.This just happens to be the first link that I came up with.
Anything with the Bacillus thuringiensis subspecies israaelenses in it works.

Here is a link that might be useful: mosquito dunks

I hung fly paper just over my plants. I also hung damp rid in the closet. they went away in a few days. I can see them on the fly paper. I don't know if the fly paper got rid of them or if they went away due to lower humity. damp rid is available at most home development super stores.

Here is a link that might be useful: damp rids websie

luisranza,

Yep, fungus gnats are extremely annoying.

As shelbyguy said, lower the humidity. You are probably keeping the soil too moist. I inevitably do it to myself each season.

I use three relatively easy methods to control / eliminate them.

1) Let the soil dry out (not enough to kill the plants though!). When the top quarter inch or so is dry, rough up the soil to disturb any eggs.
2) Set a shallow bowl of cider vinegar covered with saran wrap by the plants. Cut a hole in the center of wrap just large enough to let them get in. TheyÂre stupid to figure their way out and die.
3) I use a type of fly tape in the plant trays (photos below). Not sure if you can find them on your area but they do a great job of reducing the population. In addition, they allow you to monitor what flying pests are growing. Just check the stuck bugs to identify what they are.

Good luck,

Bill

I am having the same problem and have them in my office plants as well. I have looked up these Sticky Stiks and am only seeing availability in Canada so far.

I will definitely watch my humidity but thought that seeds like humidity to sprout so I feel like until that's all done I am going to have to rely on fly paper and the cider vinegar cocktail.

What kind of harm do they do or are they just annoying?

spensersmom,

In my experience, gnats are just plain annoying. On the other hand, thrips can be devastating. I lost most of my starts last year to a major thrips outbreak.

You have mail.

Bill