Fungus Gnats
Small black flies that hover around damp compost - mostly a nuisance, but a sign the soil is too wet.
🔍 How to spot it
Tiny dark flies, a few millimetres long, that drift up from the soil when you water or brush the plant. The real damage is done by their translucent larvae in the top few centimetres of compost, which you may spot as tiny wriggling threads in wet soil.
💥 The damage it does
Adults are harmless and just annoying, but the larvae feed on organic matter and fine roots. In seedlings and soft cuttings that root nibbling can stall growth or kill the plant; established plants usually shrug them off. A heavy gnat population almost always means the compost is staying too wet.
🧴 How to treat it
Let the top few centimetres of soil dry out fully between waterings - this alone breaks the breeding cycle. A layer of grit, sand or bark on the surface stops adults laying eggs. Yellow sticky traps catch the fliers, and a soil drench of Bacillus thuringiensis israelensis (Bti) or beneficial nematodes wipes out the larvae.
🛡️ How to prevent it
Water less often and only when the surface is dry, use well-draining compost, and empty drip trays so soil never sits soggy. Bottom-watering keeps the surface drier and far less inviting.
🌿 Plants that get fungus gnats
Anywhere kept over-watered; worst around seedlings and moisture-loving plants. These 17 profiled plants name them in their own troubleshooting notes:
Houseplants 17
Struggling to save a plant? The plant rescue guides walk through recovery step by step, and the problem solver works backwards from a symptom. This is general growing advice, not a diagnosis for a specific plant.