Select resistant varieties to minimize disease problems. Apple trees are not self-fertile; plant at least one other variety that blooms at the same time. Flowering crabapples that bloom at the same time will also pollinate apples.
Rootstock choice determines whether a tree is a dwarf, semidwarf, or standard size. Dwarf trees grow to be 8 to 12 feet tall and just as wide; semidwarf trees grow to be 12 to 18 feet tall and wide, and standard trees grow to be 18 to 22 feet tall and wide. In general, semi-dwarfing rootstocks for apples are recommended, if space permits, as true dwarfs are somewhat less hardy and therefore less suited to the coldest parts of the country.
Apples belong to the genus Malus, which also includes crabapples. Crabapples are used more as ornamentals but are also edible, albeit not quite as tasty. As mentioned above, crabapples can also be used to pollinate apples. Apples are also more distantly related to strawberries, roses, raspberries and blackberries, cherries, apricots, peaches, plums, and pears, all in the family Rosaceae.
Set bare-root trees atop a small mound of soil in the center of the planting hole, and spread the roots down and away without unduly bending them. Identify original planting depth by finding color change from dark to light as you move down the trunk towards the roots. If the tree is grafted, position the inside of the curve of the graft union away from the afternoon sun.
For container-grown trees, remove the plant from its pot and eliminate circling roots by laying the root ball on its side and cutting through the roots with shears. Don't cover the top of the root-ball with backfill because it could prevent water from entering.
Space standard trees 30 to 35 feet apart, semi-dwarfs 20 to 25 feet apart, and dwarf trees 15 to 20 feet apart. Surround each tree with a mouse guard before filling the hole completely. Water, prune, and mulch young trees right after planting.
Apples can be grown from seed, but the resulting trees do not produce good-quality fruit. For the best results, use grafted apple trees.