I have lots of small flies on and around the compost of my houseplants. Will they damage my plants and how can I deter them?
The flies sound like fungus gnats (sciarid flies). The larvae of these extremely common pests live mainly on dead organic matter just under the surface of the soil but can sometimes damage seedlings and cuttings. The adults can be killed with chemicals but I prefer to cover the soil surface with fine grit or sand to prevent the females laying their eggs. Keeping the soil surface clean and tidy and allowing it to dry a little between waterings will also help. In the greenhouse sticky yellow traps up will also reduce numbers.