Experts and BHG readers answer.
Thanks for writing. The gnats are fungus gnats and they're feedig on the peat moss in the potting mix as it breaks down. Fungus gnats aren't necessarily a problem or the sign of one, though they can be annoying.
Letting your plants dry out a little more or putting a mulch of sand over the top of the pots can help stop the gnats.
---Justin, Senior Garden Editor, BHG.com