Make sure to keep plants watered while they wait to be planted. Do not let them dry out. Drench the pots thoroughly just before planting. Let them drain for a few minutes before putting them into the ground. Pull plant out of the pot. Place the plant into the ground so the top of the root ball is just even with the ground. When refilling the planting hole, gently press the soil back into the hole, leaving no empty spaces, or air pockets underground.
Arbor Day Foundation – How to Plant Containerized Trees