By Richard Jauron, Greg Wallace
With the calendar flipping to March and spring just around the corner, fruit tree owners are thinking about blossoms and this year’s fruit crop. The key to good fruit set is to provide conditions favorable for flower bud formation, survival and pollination.
Horticulturists with ISU Extension and Outreach share cultural practices that improve a tree’s ability to begin and continue to bear fruit. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.
When should I prune my fruit trees?
Late February to early April is the best time to prune fruit trees in Iowa. Pruning should be completed before the fruit trees begin to break bud (leaf out) in early spring.
Summer pruning of fruit trees is generally not recommended. However, water sprouts (rapidly growing shoots that often develop just below a pruning cut) can be removed in June or July.
When should I spray my fruit trees with a dormant oil spray?
Dormant oil sprays are highly refined petroleum products that are mixed with water and applied to trees and shrubs to control aphids, spider mites and scale. Dormant oils destroy pests by suffocating them. When applied properly, the thin film of oil plugs the spiracles or pores through which the mite or insect breathes.
Proper timing is critical when using dormant oil sprays. In Iowa, dormant oils should be applied in late March or early April before the trees show signs of breaking dormancy (before bud break). Dormant oils applied in early March are not effective as the pests are not actively respiring at this time and, therefore, are not vulnerable to the oil’s suffocating effects. Dormant oil sprays should be applied as close to bud break as possible.
Should I fertilize my fruit trees?
It is generally not necessary to fertilize fruit trees in Iowa. Most soils in Iowa are quite fertile and can supply adequate amounts of plant nutrients to the trees.
Check tree growth to determine whether the fruit trees need fertilization. Nonbearing fruit trees should grow approximately 15 to 30 inches per year. Bearing trees should produce eight to 15 inches of new growth. (The actual amount of new growth will vary due to differences in varietal vigor.) Fertilization may be beneficial if the amount of growth is less than normal.
When fertilizing fruit trees, select a balanced fertilizer, such as 10-10-10. Apply the fertilizer in early spring before bud break. The recommended rate is one-tenth pound of actual nitrogen per year of tree age. (Tree age is the number of years since the tree was planted in the home garden.)
For example, a five-year-old tree should receive five-tenths or a half pound of nitrogen. Uniformly broadcast five pounds of the 10-10-10 fertilizer (10 percent of five is a half pound of N) in a circular band beginning about two to three feet from the trunk and extending out slightly beyond the dripline of the tree. One pound of actual nitrogen is the maximum for fruit trees 10 years of age and older.
If the lawn in the vicinity of the fruit trees is fertilized on a regular basis, there should be no need to fertilize the trees. The fruit tree roots will absorb nutrients from the lawn fertilizer. Additional fertilizer may be excessive.
Avoid fertilizing in late spring or summer as this may stimulate late summer growth that is more susceptible to winter injury. Too much fertilizer produces excessive vegetative growth and inhibits fruiting.