Answer: I suspect you are talking about fungus gnats. These breed in overly moist soil, and can be controlled in several ways. One is to allow the surface of the soil to dry out between waterings. For seed starting purposes, a good way to maintain humidity during the germination process is to begin with slightly moist soil and then cover the pot woth clear plastic to keep the soil from drying out. Once the seeds germinate, of course, remove the cover immediately.
Another method is to place a thin layer of gravel or sand on top of the soil surface. This layer will dry out quicker than the soil below and thus discourage the gnats.
Once you have solved the damp soil problem and stopped the breeding cycle, the gnats should disappear in a week or two.
Finally, you could use a soil drench such as Gnatrol to control them.
Q&A Library Searching Tips