This has exactly been my experience as well, apart from the very first grow cycle. Now I don't even bother with yellow sticky cards for monitoring gnats anymore. I don't think a fungus gnat larvae would last long with all the mites in my soil, not to mention there's not much for them to eat given the zillions of springtails who enjoy feasting on anything fungal growing near the surface. Sometimes I'll throw a handful of alfalfa feed pellets on top of my mulch, and when wet they'll mold up good and it drives those guys crazy. Heck, even a watering brings them out:
All that life is introduced simply by adding your fresh worm castings during your initial cycle. Ever see fungas gnats in a proper worm bin?
I have a procedure I follow cycle-after-cycle for mulches and cover cropping. I seed my cover crop in late flower after enough defoliation allows some light to the soil surface. Once I harvest a week or two later, that cover crop is already established. I save all the biomass I will not be drying (stems/stalks/leaves) and dry them out for later mulch. I let my soil rest for a week to let the cover crop grow a bit more, then clear enough area just to fit my new tiny plants in there. Within a few weeks, the cannabis will have overtaken the cover crop and once shaded completely the cover crop begins to decline from lack of light. That's when I take all the cut up stalks and stems (including from what I stripped the buds off later) and throw them over the dying cover crop/soil. Then the dried leaves go over this and also the yukky stuff left over from making bubble hash. I may add an inch or so of chopped straw mulch. When doing any defoliation from that point on, all the leaves or sucker branches I take off go on the soil surface. No soil is ever exposed in that pot, no matter the stage I'm in during the cycle. By the time week 7 or so of flowering comes, I just seed over the organic material with my cover crop, and miraculously it grows sending roots through that material to the humus layer underneath. And a new cycle has begun!
This is what my pot looks like right after I harvest before I cut my stocks at soil level:
Most of my cover crop seeds simply come from Walmart or Bulk Foods. I have clover, but also use lentils, mung beans, rye, and sometimes food legumes such as bush snap beans. Heck, in one cycle we harvested a couple pounds of fresh green beans before the cannabis plants shaded them out. Lol
