In the case of most fruit trees, pollination is required for the development of proper fruit production. Pollination, according to the University of Missouri Extension, is the transfer of pollen grains from the male floral part, the anthers, to the female sexual parts of the plant, called the stigma.
Self-fruitful and cross-pollinating trees pollinate differently, says Purdue University. Self-fruitful plants can use pollen from the same cultivar or tree variety, while cross pollination is the transfer of pollen from one fruit tree variety to another. In cross pollination, a tree's own pollen will not fertilize its flowers, so another tree is required. A compatible tree must be found for suitable cross-pollination.
The king blossom, which is the largest blossom and first blossom to open in a fruit set on a tree, should be pollinated. When planting trees in a yard, two semi-dwarf apple varieties planted within 50 feet of each other that bloom at the same time ensure pollination between the trees. In commercial production, pollinating plants are placed every few rows to ensure fertilization.
For pollination, bee hives are often kept to pollinate trees in commercial orchards. Bees use the flowers of fruit trees to produce honey. As they move from plant to plant, pollen sticks on their legs. They transfer the pollen between flowers, pollinating them as they do their work.
When semi-dwarf varieties are present, one large bee hive of around 15,000 to 20,000 bees is enough for one acre of land. Two hives per acre are used when planting of trees is dense. Bee hives are best put into place once herbicides have been used to kill dandelions and other flowering weed plants in the orchard area.
Poor pollination is often caused by a lack of pollen reaching flower sets in time or frost during the period where trees are in bloom. Bees used to pollinate trees travel slowly during temperatures below 50 degrees F, as well as in rainy or windy weather. Insecticides sprayed early in the season may drift onto blossoms, killing bees that land on the flower for pollination purposes. This also affects the effectiveness of cross pollination.