Little Black Flies?

Zazen999

Water from the bottom; they live in the top damp compost. No damp compost = no flies.

Blackpool_Saver

I had this at my other house, hideous, mine was from plant soil too, the plants went out, shame but not worth the health risk.
We even thought it was the drains and put all sorts down until finally figuring it was the plants..

Maria575757

I'm sure these are Fungus Flies. The larvae live in the bark of the soil - once hatched they will live for approx 4 - 5 days. You will often find that the flies 'leave home' after you have watered your plants as they love damp soil. There are several ways to get rid of them.
1) Repot the plant using sterile potting compost free of bark chips. Give ample drainage in the soil by adding products such as perlite.
2) Only water your plants when they are dry - the plant will survive being dry for a time, but the fruit flies won't.
3) Slice some raw potato and lay on the surface of the soil - this attracts the larvae which burrow to the top into the potato. Replace the potato after 24 - 48 hours and keep doing so until you no longer see signs of the flies in them. Yuk!
4) Cover the top of the soil with approx 1/2 to 1" of sand. this acts as a barrier to the flies and they have to stay together with the larvae in the soil and will die within a week.
5) If you don't want to do any of the above buy a carnivorous plant (such as bladderwart) and put alongside the affected plants.
Hope that helps.