Just because you don't see them flying doesn't mean they aren't still alive in your soil and/or eating your roots. I use mosquito dunks. You can get a 6 pack of dunks at Lowes for under $10 and it takes about 1/8th of a dunk to treat a 5 gallon bucket. The only problem is that you are supposed to put the dunk in water, so IDK how you'd do it with soil, but it works great in my DWC