The several cultivars of apples (Malus domestica) are self-sterile or even self-unfruitful, meaning that they will not bear apples unless they get pollen from a compatible number of apple tree or even a crabapple tree. There are a few apple tree types that may bear fruit without cross-pollination, but they perform poorly and planting them is not recommended. Apples can be grown in U.S. Department of Agriculture plant hardiness zones 3 through 8.
Quantity Of Trees Required
At least 2 apple trees of different varieties that bloom at precisely the same time are needed for good pollination. Planting two McIntosh apple trees will not do. You have to match one McIntosh with a compatible apple number, say a North Spy or Honeycrisp. To guarantee proper pollination, plant two semi-dwarf varieties at least 50 feet apart; plant dwarf trees over 20 feet apart.
Overlapping Bloom Times
Apple blossoms grow in clusters. Apple trees grow more apples if a bee or other insect carrying complementary pollen lands on the most significant blossom in a cluster and the first to start. This is called the king blossom. To guarantee proper pollination, matching trees need to blossom and yield pollen in precisely the same time. To help you choose complementary apple trees, nurseries which sell transplant seedlings typically have charts that record overlapping bloom times for a variety of cultivars. The pollen from crabapple trees often offered as ornamentals will pollinate conventional trees.
Some nurseries listing some apple varieties since being self-fruitful. These include Empire, Gala, Golden Delicious, Granny Smith, Rome, Jonathan, Jonagold, Liberty and Rome. While these varieties may yield a few apples if they planted alone, it is not recommended; without cross-pollination they generally yield few apples of inferior quality. Some apple varieties produce sterile pollen and cannot be used to pollinate other trees. These include Baldwin, Boskoop, Bramley’s Seedling Crispin, Creston, Gravenstein, Jonagold, Mutsu, Roxbury Russet, Spigold, Stayman, Wealthy and Winesap. Apple varieties that produce sterile pollen require pollen from other trees.
Pollinating a Single Tree
There are two ways to pollinate a solitary apple tree. You can put branches together with open, fresh blossoms of crabapple or complementary apple types in buckets and hang the buckets in the tree. You can also cleft-graft 6- to 8-inch-long branches of a compatible apple number onto your tree.