Most fruit trees require cross-pollination (the pollen of a different but compatible variety) to yield a crop of fruit. Pears, sweet cherries and Japanese plums fall into this category. Other fruit trees, such as peaches, figs and sour cherries are self-fruitful, meaning they yield fruit from their own pollen. Another group of fruit trees, including most apples, are semi self-fruitful. Trees in this group will yield an adequate crop without cross-pollination, but yields increase with cross-pollination.
Cross-pollination is accomplished by planting two or more varieties side by side or grafting two or more varieties on one trunk. The cross-pollination varieties must bloom at the same time and be compatible with one another. The length of the blooming season varies from 7 to 15 days depending on the fruit, varietal strain and weather. Cold, windy and wet weather can prevent bee activity and therefore hinder cross-pollination during fruit blooming.
Apples and Pears
In order for apple and pear trees to produce fruit, there has to be a second tree for cross-pollination to occur. As long as a second tree is within 500 feet of the first, pollination should take place. If your apple or pear trees are not performing to satisfaction, the following list will help you trouble-shoot:
Cool, rainy weather conditions during flowering
Unfortunately, other than hoping for better luck next year, there is nothing that can be done.
Old, unproductive trees that don’t flower
Generally, apple and pear trees have a productive lifespan of about 30-40 years. Trees can be rejuvenated by removing old, unproductive growth and allowing new growth to replace it.
A poor crop the year after a bumper crop
Some apple varieties tend to perform biennially, with a great crop one year, not so great the next and a better crop again the third year.
No trees of the same genus nearby
It is always best to pollinate fruit trees of the same genus with each other (apples with apples, pears with pears) but pears can cross-pollinate with apples as long as both trees bloom at the same time.
The other cultivar in the yard is sterile
Some (but not all) crabapple trees work for cross-pollination. A few varieties have sterile pollen.
Lack of pollinating insects
Try adding to your flowerbeds. Most flowering plants are guaranteed to attract bees. The annual herb Borage and the perennial Bee-Balm (Monarda) are especially good for this purpose. Due to their flowering times coinciding with those of many fruit trees, marigolds, pansies, spurge, trollius and arabis are the best choices.
The trees are of the same variety
Clones will not pollinate each other. For example, a Norland apple tree cannot pollinate another Norland apple tree.
European apricots are self-pollinating. Manchurian and Siberian apricots fruit more dependably with other apricot varieties or Nanking cherries.
Cherries and Plums
Sour cherries are self-pollinating. In order for cross-pollination of the remainder of cherries and plums to occur, it is essential that they bloom at the same time. Many chokecherries will also aid in cross-pollination. Plums must be from the same region of the world to cross-pollinate (European plums with European plums, Asian with Asian, etc.). The closer the relationship between species, the more abundant the fruit will be.
Grapes are self-pollinating. Cross-pollination is not essential, but some hybrids may have non-viable pollen. Planting two or more varieties will solve the problem.
Blueberries are self-pollinating but two or more varieties result in better yields and larger berries.
Currants and Gooseberries
Currants and gooseberries are self-pollinating. Excellent fruit production can be obtained with just one plant. If currants are grown near gooseberries or jostaberries, however, yields can be even better.
Strawberries and Raspberries
Strawberries and raspberries are both self-pollinating.
Both male and female plants are required to produce fruit. You need at least one of each plant but a male can cross-pollinate up to 8 females. Plants must be 2-3 years old before they can produce fruit.