Hi Susan –
Yes you can use poison-free GoGnats as a soil-drench or with hand-feeding. Apply 2 times the first week and reapply every 2 weeks as needed.
DIRECTIONS FOR USE:
General Maintenance: 1 tsp/gallon
Infestations: 2 oz/ gallon. Drench the soil until solution starts draining out of the bottom. Return to General Maintenance schedule.
May be added to most liquid fertilizer feeding solutions.
Hope it helps!