Fruit Set In Fruit Trees
by Dr. Robert Black, Consumer Horticultural Specialist

Many of you have probably planted fruit trees and have been disappointed when they failed to bear fruit. Fruit trees generally bear fruit when they become old enough to blossom freely, provided other conditions are favorable. Pollination, cultural practices, and environment greatly influence the plant's ability to bear. Any of these factors alone or in combination can prevent fruit set or cause flowers not to develop and fruit to drop prematurely.

Growers do have some control over most of these factors. Even though trees blossom freely, most of them will either fail to set fruit or they will shed most of their fruit prematurely if adequate pollination does not occur.

Some fruit trees have "perfect flowering" blossoms with both male and female parts. When they bear fruit as a result of pollination from their own blossoms they are said to be "self-fruitful."

Unfortunately, many fruit trees with perfect flowers do not set fruit with their own pollen, but require pollen from another variety. Varieties such as these are called "self-unfruitful."

In some fruit varieties the pollen producing or staminate (male) blossoms which never produce fruit are borne on separate trees from the pistillate (female) or fruit producing blossoms. In such cases, it is necessary to have at least one tree with male flowers to serve as a pollinator.

Trees with only staminate flowers will normally pollinate a number of trees with female blossoms. The persimmon is a good example of this type fruit. Varieties that produce male and female flower parts on separate trees should not be planted whenever other acceptable varieties are available.

Citrus, figs and peach trees are usually "self-fruitful" and require no other varieties for pollination. Most apples, pears and plums are "self-unfruitful" and require two or more varieties in the planting. To assure adequate pollination, the varieties should have the same bloom period.

Soil fertility has been found to influence the ability of trees to hold and mature their fruit. Over-fertilization, especially too much nitrogen causing excessive vegetative growth, can cause fruit to drop. During extremely dry periods, fruit that were not completely pollinated will generally drop before those that were adequately pollinated.

Most deciduous fruit trees (peach, plum, etc.) require a specific number of hours of cold temperatures (chilling requirement) during the winter in order for the flower buds to open in the spring. If they fail to receive this needed cold, the tree will not produce fruit. The chilling requirement differs greatly among varieties. Therefore, it is important when selecting fruit trees to choose varieties with low chilling requirements.

In some instances, insects and diseases may cause fruit drop. In other cases, deep cultivation too close to trees has been cited as the cause of fruit drop.

Adverse weather conditions at time of bloom may interfere with pollination and result in fruit drop. Also, extremely low temperatures during dormancy can cause bud injury and prevent fruit production.