Hello. I use Doktor Doom Pyrethrin Insecticide Power. Made from chrysanthemum flowers. It's non toxic to humans, pets and plants. I spray it about 2 inches around the stem and up the stem a bit. The gnats like to run up and down the stem so that running action gets some power on them. You can always goggle the product to see if it's something you want to use. You can get it at most garden stores. Chuck.