Adults versus larvae
Adults
Aromatiny dark flies with long legs, hovering near the soil and lower canopy
Larvae
Aromacreamy with a shiny black head, living about 1 to 3 inches (2.5 to 7.5 cm) down
Trays
Aromaafter a watering you may see larvae wriggling in runoff from shallow pots
Harm
Life cycle
Eggs
females lay on moist mix near the stem
Hatch
larvae appear in about 4 to 10 days, then pupate in the medium
Speed
egg to breeding adult is about four weeks; females lay hundreds of eggs
Indoors
breeding runs year-round when the surface stays wet
Dry the surface
Check
inspect outdoor plants for adults or larvae before they come inside
Screens
keep window screens on so adults cannot fly in
Barrier
cover the pot with cloth, cardboard, sand, coco mat, or a rockwool lid so eggs have nowhere to land
Watering
let the top inch (2 to 3 cm) dry as much as the plant will allow
Top dress
a light, draining layer of vermiculite, perlite, or dry diatomaceous earth helps that surface dry
Controls the book lists
BT
Bacillus thuringiensis products aimed at gnat larvae
DE
dry diatomaceous earth punctures soft larvae; it fails when wet
Mites
soil-dwelling Hypoaspis predators hunt what they can catch
Nematodes
Heterorhabditis and Steinernema species enter larvae and kill from inside
Also listed
cinnamon oil or tea, pyrethrum, and spinosad as grower options