Apples are self-incompatible and must be cross-pollinated. Pollination management is an important component of apple culture. Before planting, it is important to arrange for pollenizers - cultivars of apple or crab apple that provide plentiful, viable and compatible pollen. Orchard blocks may alternate rows of compatible cultivars, or may have periodic crab apple trees, or grafted-on limbs of crab apple. Some cultivars produce very little pollen, or the pollen is sterile, so these are not good pollenizers. Quality nurseries have pollenizer compatibility lists.
Growers with old orchard blocks of single cultivars sometimes provide bouquets of crab apple blossoms in drums or pails in the orchard for pollenizers. Home growers with a single tree, and no other cultivars in the neighborhood can do the same on a smaller scale.
During the bloom each season, apple growers usually provide pollinators to carry the pollen. Honeybee hives are most commonly used, and arrangements may be made with a commercial beekeeper who supplies hives for a fee. Orchard mason bees are also used as supplemental pollinators in commercial orchards. Home growers may find these more acceptable in suburban locations because they do not sting. Some wild bees such as carpenter bees and other solitary bees may help. Bumble bee queens are sometimes present in orchards, but not usually in enough quantity to be significant pollinators.
Symptoms of inadequate pollination are small and mishapen apples, and slowness to ripen. Count the seeds to evaluate pollination. Well pollinated apples are the best quality, and will have 7 to 10 seeds. Less than 3 seeds will usually not mature and will drop from the trees in the early summer. Inadequate pollination can result from either a lack of pollinators or pollenizers, or from poor pollinating weather at bloom time. It generally require multiple bee visits to deliver sufficient grains of pollen to accomplish complete pollination.