So nematodes will live in soil a while! If u reuse soil u wont need to reapply every time! Last run before current 1 I hadn’t applied any to small tent and had only applied to big pots like 4-5 months earlier and wound up getting gnats in small tent but big pots that had gotten the 1 dose never had any! Unless soil dries out for a long time or they have no food source for long enough that they die off they will hang around!