You can use potting soil or a mix of compost and regular garden soil to plant your container grown apple trees.
Place some gravel or broken clay pot shards at the bottom of the container to facilitate drainage prior to planting the tree.
If you have a bare root tree, trim the roots so they’ll fit in the container easily. If the tree came in a nursery pot, check to see if the tree is root bound. If so, loosen the roots up and trim them to fit in the pot.
Fill the bottom of the pot with soil atop the gravel and situate the tree so the graft union (the bulge towards the bottom of the trunk where the tree was grafted) is level with the lip of the pot.
Fill in around the tree until the dirt is 2 inches (5 cm.) below the lip of the pot. Stake the tree to give it some support. If you want, mulch on top of the soil to aid in moisture retention.
Cut the newly planted apple back by 1/3 and water the tree well until water runs from the holes in the pot. Feed the plant during its growing season, especially since some nutrients run out of the drainage holes.
Water is very important when growing apple trees in pots, or anything in pots for that matter. Pots tend to dry out much faster than things grown in the garden proper. Water the tree at least twice a week, daily during hot months. The smaller the container, the more often you need to water since the surface area is so small; it is difficult to get enough water in and to the roots.
Drought stressed trees are open to insect and fungal infections, so keep an eye on the watering.