1-2 inches deep. I was advised by an old guy who's planted 1000's to plant seed flat the way the whole fruit would rest if it fell to the ground of it's own accord. Gravity works on root and shoot to send them in their respective directions. The same guy demonstrated grafting mango using a plain old razor knife, a random seedling found under a mango tree, and a strip of plastic cut from an old wal-mart bag. The graft appears to have taken so I think he knows what he is doing. He likes to use saliva as a probiotic on scions.