Apple trees may seem to produce luscious fruit on demand by magic. However, whether you have full-sized or dwarf apple trees in your yard or garden, there is no magic involved. It is a miracle of nature, of course, but several aspects have to fall into place to provide pollination.
Apple trees do not self-pollinate. The technical term for this is "self-unfruitful." This means it takes more than one variety to produce fruit because each variety does not pollinate itself. If you have a small space and only want one variety, at least one crabapple tree is enough to provide an extra "variety" for pollination.
Plant trees at the right distance to ensure proper growth and good contact during pollination. Plant trees at least 20 feet apart to give them plenty of room to grow and spread. However, keep trees no farther than 100 feet apart to guarantee pollination.
To get the best crop, blooms should blossom at the same time on both varieties. Pick apple tree types that bloom and mature at the same rate. Some apple trees are early bloomers; some are mid-season or late bloomers.
Birds and Bees
Actual pollination happens when birds, bees and even wasps fly about in the leaves. Honeybees perform a complex function that pollinates the tree while they gather nectar from flowers to produce delicious honey. All that is necessary is pollen attaches itself to the fuzz or feathers of passing insects and birds and lands on a nearby apple tree of another variety. For gardens with many apple trees and more than a casual desire for fruit, keeping one or two beehives on site is essential. If you do not have a hive or want one, grow plants that attract bees in the general area of the trees. These include flowers, clover and even dandelions.
For extremely small yards with only one tree and no nearby crabapple tree, the only other option is grafting. Attaching another variety of tree to the original tree is successful if done correctly.
You can try a simple but effective trick if you have no other options and can get your hands on some crabapple or other variety of apple tree branches. Place a few blossoming branches in a large bucket of water to keep them fresh for a few days, and place them in the direct vicinity of your existing tree, preferably directly under the canopy. You can also hang the branches in the tree itself, although they won't stay fresh as long as they would in a bucket of water. The hope is that bees will visit the branches and your apple tree, thereby pollinating the tree.