Pollination is when grains of pollen are transferred from the male part of the flower to the female part. Pollen is ordinarily spread by bees flying from blossom to blossom. After pollination, seeds develop and the fruit grows. Some fruit trees pollinate themselves. Others need pollen from other trees, which is called cross-pollination.
When Trees Need Pollen
Most trees won't bear fruit using their own pollen or pollen from another tree of the same variety of fruit. If flowers are not pollinated, they may drop immediately after they bloom. Trees that are self-pollinating will generally produce more fruit if they receive pollen from trees bearing a different variety of the same fruit.
Trees Needing Cross Pollination
Most apple, pear and sweet cherry trees need cross-pollination. Apricots, nectarines and peaches usually pollinate themselves, but they will produce more fruit if they are cross-pollinated.
Fruit trees used for cross-pollination should be those varieties that bloom at about the same time. A tree that blooms in mid-season will sometimes overlap with those that bloom earlier in the season and those that bloom later.
Bees Are Important
Bees carry most of the pollen from tree to tree. One honeybee may visit 5,000 flowers a day, carrying pollen on its body hairs from blossom to blossom. Bees fly shorter distances if it is below 50 degrees F or if it is rainy or windy.
Wild bees will ordinarily do the job for home planting, but you can often rent hives of disease-free bees. Move the hives into your orchard when your trees have started to bloom. Use about two hives per acre of trees. When the blooming is finished, remove the bees. You can buy pollen from commercial suppliers and put it in inserts at the entrance to the hives. Use about a teaspoon of undiluted pollen every several hours, or about 1 1/2 ounces of pollen per acre of trees. When the bees leave the hives, they'll carry pollen that your trees need.
You should mow dandelions or remove them with a herbicide before you release bees into your orchard. Do not spray your trees with insecticides when there are bees in the area.
To ensure cross-pollination you need to plant at least two trees. For best results, plant them at least 50 feet from each other. Plant dwarf trees 20 feet from each other. If there are enough bees in the area, your trees can often receive pollen from neighboring trees.
If you have a solitary fruit tree that needs pollen, you can put branches of fresh blossoms with compatible pollen in buckets and hang them in your tree. If you have a solitary tree, you can also graft 6- to 8-inch sections of a compatible variety onto the terminal branches of your tree.
Researching Trees to Plant
You need to do your homework to find the correct mix of cultivars that have compatible pollen. University extension services and gardening books are good places to find combinations of trees for cross-pollination. Many universities post their recommendations on the web.