Here is my two cents worth, on your question. Plant now in it's natural soil ( nothing added ). Now next spring if you want to mulch or add fertilizer OK. Now the purple plum around here, in West Tn. will grow in just about any soil around, without fertilizer.
Norm

Norm is right. You don't need to add anything into the planting hole except for natural soil. Dig a dish shaped hole about three times the diameter of the pot the tree would be in if it were to be planted into a container. This will allow the roots to get a good start. I would advise adding mulch on top, now. Use about 2" to 3" covering the planting hole or even further out if you want. You can use 2 to 4 sheet layers of newspaper to suppress weeds under the mulch. Don't mulch all the way to the trunk (especially no mulch volcano). Try to get as much root as you can with the suckers. If you have rooting hormone handy, that wouldn't hurt, but it's not necessary. Finally, I would not fertilize the tree unless a soil test indicates a need for it. Fertilizing trees rarely helps trees and often has a detrimental effect.