The larvae of fungus gnats are tiny white worm-looking insects. They come up to the surface of the soil at watering. The larvae feed on organic matter (meaning stuff that was once alive), but will also nibble on tender new roots.

You are probably using a potting mix that is too mucky/fine-textured/peaty/slow draining. Course textured, fast draining mediums cannot foster a rampant fungus gnat population. But that's for next time...too late to do anything about your mix at this point.

Fungus gnats (the larvae) thrive in a mucky potting mix that is kept too moist for long periods of time. Allowing the containers to dry out somewhat may help SOME...but is not the solution to this problem.

I suggest that you google Gnatrol or mosquito dunks, both of which contain the biological control for fungus gnats (and mosquitoes, their close relatives). Using one of these products when you water will kill those larvae.

The simplest way to keep Fungus Gnats from appearing is to allow the potting soil to dry out between watering.

Here is a link that might be useful: About Fungus Gnats

Thanks guys, for a moment I got very freaked out..

I sprayed them with the safer, seems to work like a charm, within minutes it was a gnat genocide.

But if I let the water dry up.. wouldnt it harm my plants?

The Safers will kill the flying adults, but not will effect any of the larvae not directly in contact with the solution, and certainly not effect any eggs that the adults deposited into the soil.

Some people think that the best solution is to let your containers dry out, but this is simply not so....once a population becomes firmly established. Fungus gnats can thrive perfectly well in potting mediums that are not excessively moist, just adequately so.

It is, however, a very good idea to be certain that you aren't keeping the medium overly moist at all times. Don't let your container sit in water, for example. Again, in the future, consider a potting mix recipe that allows you to water freely without staying soggy, ever.

Some other things you can try, if you don't want to go with the Gnatrol or 'dunks' route, is to cover the surface of your containers with a layer (quarter to half inch) of part coarse builders sand and part horticultural grade Diatomaceous Earth (DE), which can be found in the garden center. Do not confuse horticultural/food grade DE with the stuff that is used to filter pools.

If one were to allow the potting soil to totally dry that may well affect the plant growing there. However, if one follows that advise in the link I provided above and allow the soil to dry as much as possible (you can easily check moisture levels in containers by inserting your index finger to the first knuckle) without allowing the plant to suffer. Numerous people with phDs in horticulture and soil science recommend allowing the soil to get dryer then the larva of the Fungus Gnats need to live in as one way to control them. That is an inexpensive means of control, does not require purchasing some product that will be about as effective at control as allowing the soil to dry out some.

I have tiny white worms only under my knockout roses. What do I do?