In most cases, pollinating fruit trees requires at least two trees, and they should be different varieties, as discussed below. The trees should be within about 50 feet of each other, because pollen is too heavy and sticky for the wind to carry, leaving bees to do the job.
Self-fruitful (or self-fertile) trees vs. cross-pollination
In order to ensure that your fruit tree is pollinated, choose a self-fruitful variety or be sure that there is another compatible tree nearby (a pollinator that blooms when your tree blooms).
Self-fruitful (self-fertile) trees are those that produce fruit with their own pollen or with pollen from the same cultivar (cultivated variety). Self-fruitful trees don’t necessarily require another tree for pollination, although they may produce better if there is more than one tree in the area.
Most fruit trees require cross-pollination: that is, they need pollen from another tree, which must be a different cultivar. Triploids are cultivars that will not pollinate other varieties—or themselves: they must be pollinated by another variety.
Finding the appropriate pollinator for your fruit tree requires a little research. In general, early blooming trees can pollinate each other, and mid- and late-blooming trees can pollinate each other. Early and late-blooming trees can’t pollinate each other because their bloom times are too far apart: the early bloomers will be finished blooming before the late-bloomers start. The Raintree Nursery catalog provides pollination charts showing which varieties can pollinate each other for each type of fruit—apples, European pears, Asian pears and plums.
Apples don’t pollinate themselves. You must have two different varieties. In addition, apples don’t pollinate other fruits. The following apple varieties are triploids—that is, they don’t pollinate any other apples: Gravenstein, Jonagold, Red Boskoop, Shizuka, Karmijn, King and Bramley.
European pears need a pollinator. Because pear blossoms are relatively unattractive to bees, plant pear trees near each other to promote pollination.
All varieties are good pollinators, but each tree needs to be pollinated by a different variety. Asian pears bloom before European pears, but late-blooming Asian pears may pollinate early-blooming European pears. The Shinseiki may be partly self-fertile.
The following European plums are self-fruitful (self-fertile): Golden Transparent Gage, Purple Gage (partially), Cambridge Gage (partially), Italian Prune, Longjohn (partially), and Stanley. The following Japanese plums are self-fertile: Hollywood, Methley, Shiro (partially).
The following sweet cherries are self-fertile: Black Gold, Lapins, Sweetheart, Vandalay. These tart cherries are self-fertile: Almaden Duke, English Morello, Montmorency, and Surefire.