Pollination is the transfer of pollen from the stamen, the male part of the flower, to the pistil, the female part of the flower. Pollen is moved from one blossom to another by wind and rain or by bats, bees and other insects. Bees are by far the best pollinators. Pollination is crucial for the production of fruit. Flowers of a tree may bloom, but unless they are pollinated, they will remain infertile and unproductive.
The male anther, located at the tip of the stamen, contains pollen; female stigma, the sticky tip at the end of the pistil, collects the pollen. Some species of fruit trees have blossoms of different sexes. Other species have what are called “perfect” flowers, meaning that they contain both anther and pistils.
Trees that require pollen from another tree of the same variety or that set fruit without pollination are called self-fertile, self-fruitful or self-pollinating. Some trees with perfect flowers still need pollen from another tree. Trees that need pollen from a related cultivar are called self-unfertile or self-unfruitful. Trees with pollen needed to fertilize a self-unfruitful or self-sterile trees are called a pollenizers.
Planting for Pollination
If other trees are needed for pollination, they should be planted nearby. If trees are separated by more than 100 feet, it is unlikely that bees carrying pollen will fly back and forth between them. The closer trees are, the more pollination will occur.
Bees are the best pollinators in an orchard. Bees need nectar for energy and pollen for protein. As the bees fly from blossom to blossom collecting nectar, they carry pollen on the tiny hairs that cover their body. When bees carry pollen from one blossom to another blossom, the second blossom is pollinated. There are solitary bees, honey bees and bumble bees. There are hundreds of species of solitary bees, the queens of which do their own foraging. Bumble bees forage at lower temperatures than other bees, and they can fly when it is windy. By far the most common and productive pollinating bee is the European honey bee (Apis mellifera L.) found all over the world. Parasitic mites have decimated colonies of wild bees. Domestic pollinating honey bees, Apis mellifera L. and related species, are kept in commercial hives that are rented out to orchards. Beekeepers move two to four hives on pallets aboard trucks. The more trees in an orchard, the more bees are required for pollination.
Other Pollinating Methods
If it is impossible to plant nearby trees for pollination, branches of a necessary pollinating cultivar may be grafted onto a tree. Branches containing flowers from a pollinating tree may be hung from branches or placed in a nearby jug or basket. This should be done in the early morning when it is cool and the bees are out and about.
Some apples, pears and plums are self-fruitful and can be planted alone. This sometime varies by geography. Most apricots, nectarines, peaches and figs are self-fruitful. All sour cherries are self-fruitful. Sweet cherries, many apples and some apricots, peaches, pears and plums are unfruitful. Gardeners need to pay attention to pollination requirements when they buy seedlings for planting.