Organic/safe insecticide?

I was thinking that on my next grow, I'd like to douse the soil with something to kill any insects/larvae before planting. Is there an inexpensive product that will do this and is safe to use?

Not really.

Sun baking it when its dry. Black trash can. 108° summer temps. But when you rehydrate it. Fungus come out of nowhere and will still gang bang your pot.

It's not organic but Azamax works for me. Sprayed on the top of the (soil).

Well sort of.... using neem seed meal as a soil amendment helps reduce likelihood of leaf munchers like thrips but it’s not really an insecticide. To prevent gnats a sprinkled layer of diatomaceous earth and/or sand on top of the containers keeps them from laying eggs. If there are mature flying gnats present yellow sticky traps can help control them. Prevention of course is always easier than treating an infestation.

Depends what you're trying to kill. Mosquito dunks work good for gnats.