Gnats are by far the easiest garden pest to eleminate without the use of any chemicals,go to home depot or a hardware store & buy a dozen sticky fly paper's that you can hang above the plants,nothing fancy like the little things that look like bird houses just plain ole fly paper,this will catch an enormous amount of gnats very quickly.
The next step is to increase air circulation at the canopy level & below,this will drive the gnats to where the air current is not so strong & right into the fly paper.
Next you want to scarify the top inch or two of the soil,by scarifying i mean you want to physically get your fingers in the soil & loosen the top layer until its very fine particles,do this every day,scarifying the soil will bring any & all gnat larve to the surface where they will bake under the lights & die.
Keep this regime up for 1 week & you will be gnat free,after 2 weeks every last larve will be destroyed & you can continue in peace.
Scarifying the soil is also very good for the plants oxygen uptake,compacted soil does not hold as much oxygen,this process of having your hands in the soil daily also aids you in the learning process of watering the plants,by having your fingers in the earth daily you quickly get a feel for the moisture content of the soil.
