Yard and Garden: Flowering Fruit Trees

AMES — Ideally, a fruit tree will begin to bear when it becomes “old enough” to blossom freely. This is not always what happens, however. The characteristics of the tree, its environment, the cultural practices used and the weather all affect a tree’s ability to begin and continue to bear fruit. There is not much that can be done to influence the weather, but there are ways to control the other factors.

The key to avoiding poor fruit set is to provide conditions favorable for flower bud formation, survival and pollination. Iowa State University Extension and Outreach horticulturists answer grower questions about flowering fruit trees. For more information, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

My apple tree didn’t bloom this spring. Why?

The lack of flowers on small, recently planted trees is usually due to their age. After planting, most dwarf and semi-dwarf apple trees don’t flower and bear fruit for three to five years. Standard apple trees may not bear fruit for five to 10 years. Fruit trees have to grow and mature before they are capable of flowering and fruiting.

The lack of flowers on well-established trees may be due to the tendency of fruit trees to bear fruit in two year cycles, consisting of a large crop followed by a small crop. This is referred to as alternate or biennial bearing. Alternate bearing occurs in almost all tree fruits.

The flowers that produce next year’s crop are initiated during the development of the current season’s crop. When a fruit tree is producing a large fruit crop, most of the tree’s energy is utilized for fruit development, little energy remains for flower initiation. As a result, a fruit tree often produces a small number of flowers and fruits when preceded by a heavy crop the previous year.

To discourage alternate bearing, home gardeners should thin apple and other fruit trees when fruit set is heavy. Hand thinning of apples should be done within six weeks of full bloom. Leave the largest apple in a cluster unless it is damaged. After thinning, apples should be spaced about 8 to 10 inches apart on the branches. Pears, apricots and peaches also may need to be thinned. Fruit should be spaced 6 to 8 inches apart on the branches. Plums will generally thin themselves.

My peach tree didn’t bloom this spring. Why?

Peaches are not reliably cold hardy in many parts of Iowa. It is possible to grow ‘Reliance’ (yellow flesh, freestone), ‘Contender’ (yellow flesh, freestone) and ‘Polly’ (white flesh, clingstone) in the southern one-third of Iowa.

Newly planted peach trees usually don’t bloom for two or three years. The lack of flowers on well-established trees is likely due to cold winter temperatures. Winter temperatures of -20 degrees Fahrenheit will destroy the flower buds on peaches. (The flower buds on apples, pears and sour cherries can tolerate temperatures of -25 to -30 F.) Most parts of Iowa experienced temperatures of -20 to -25 F during the winter of 2017-2018. The flower buds on established peach trees were likely destroyed by cold winter temperatures.

Will fertilizing a young fruit tree encourage it to flower and produce fruit?

It is generally not necessary to fertilize fruit trees in Iowa. Most Iowa soils can supply sufficient amounts of nutrients to fruit trees. Fertilization may actually encourage excessive vegetative growth and inhibit or delay flowering and fruiting.