Gnatrol has to be used as a soil drench to be effective and is not good for the plants imo. Just put a nice 1/2"+ of perlite on top of the soil, allow top 1" of soil to become dry and fungus gnats won't be a problem. The adults will still come but you won't have an outbreak. Tap on the perlite with your hands and do much damage to the adults under and between. The adults won't stay either if you keep it dry as possible on top.