I've been playing religiously with neem cake for the last 8~9 months. I grow in Airpots, Autopots, WaterFarms, AquaFarns, (just a smaller 25 L WaterFarm) and sometimes smartpots. Mediums are soil, Mapito and coco. Ratio I use of neem cake is 50 g per 25 l of medium, except in the WaterWater/AquaFarns when not using coco but clay pellets because I'm not entirely sold on the idea of adding neem cake to a water reservoir.... It's of course only a matter of time before I can't resist to do that too.... Just to see if it's really true that curiosity killed something feline....
I haven't seen a soil breeding insect hanging out ever since, and I grow with an open window all year to keep temperature down, wide open in the summer/insect season(and no, it can't be screened, it's a large Velux window that swing open inward vertically).
I hasten to add that the neem cake had been combined with Diatomaceous Earth(DE). The DE dosage is the same plus whatever it takes to dust the top surface for a decent crust, say another 25 g or so.
Both are mixed into the top 4-5 cm of medium, then I spray/water the surface to wet it, give it a good final dusting on the wet surface,which forms a nice water penetrable crust when dry. This is especially nice with the Autopots, as it's only the first 2-3 weeks they get dihydrogen monoxide from topside, but it also assists in watering an Airpot or smartpot and keep the bowl shaped topsoil that way....
Both products are easily available in EUR, very cheap and can be ordered no sweat from ebay(search for niemsamen..... Which is neem cake in German), here's where I got the neem cake
http://m.ebay.de/itm/350840747750?_mwBanner=1 these blokes also has DE, although I bought my 5 kg for 30 euro from a local horse haberdashery, apparently horses and pretty much all other mammals get greater mileage with a bit of DE added to the tank ,according to the purveyors, so take that with a grain of salt...... Nah, I don't mean literally ..... Lol
Neem cake has a distinct garlic like smell, once you've smelled it you won't forget, but it doesn't linger long, day after application it's completely gone.