As Chuck says, make sure the graft is well above the surface, so you don't lose the benefits of the rootstock, indeed you'd likely kill it.
I'd also recommend a 2" layer of woodchip mulch around it to a radius of 3 feet, and keep it well watered for the first year.
Unlike small plants, where the biggest fault is overwatering, 1/3 of new trees die within the first year for want of water.
You could also buy a small pack of mycorrhizal fungi, mix with water, and water into the planting area; it would have been better to have added this to the planting hole immediately prior to planting, but this will still help.
