I am writing this up on here as the quantity and varied methods of planting an apple tree have made it become a difficult subject to allow a conclusive methodology. The following is my personal preferred method for establishing an apple tree in Cornwall, it would be great to hear what other professionals on here would criticise or what different techniques there are:
Bare Root - Available from mid October through to March, bare root stock is usually considerably better in establishing quickly. I personally think that a February planting is best. I always graft onto a mm 106 semi dwarf, which seems to do very well here for the Cornish Varieties.
A square sided hole, dug to a depth of about 400mm to 500mm is best. The turf cut out and removed to compost or to fill that nagging hole.
The bottom of the hole is watered with about 30mm of water. It is good to do this to test the drainage of the hole and to asses the soil condition.
The tree is then placed within the hole. It is important to ensure the roots are facing from a horizontal to a downward angle. If they are not, it is possible to prune the roots accordingly:
Prior to backfilling with loose soil, staking above and below the graft is essential. Position the stake against the tree in the hole, then remove the tree and drive in the stake. Lightly hammer it in, (a lightweight stake or bamboo cane is all that is required on young trees).:
Most tree ties available for sale are adequate or an old piece of bicycle innertube. The tie should allow for some movement of the tree, (tightening too much can be catastrophic), and should allow the tree to move slightly in the wind thus encouraging the roots to strengthen.
Backfill to top of the hole, then gently, push down the soil around the base. This should allow for 50mm or so more loose material back around the base of the tree, which should not be squashed in.
Personally I will always try and opt for a transparent tree spiral for protection against rabbits, if I can get hold of them. This must have an adequate gap between the lower branches and the top of the spiral. A permeable mulch mat is essential for most sites with a good, with a inane mulch applied.
The second year is the best time to remulch using a well rotted 'horse manure' compost or similar, nothing too rich. It is becoming quite a common problem to see many overfed trees.