Digging In: Advice on an Ailing Hawthorn Tree, Pruning Crape Myrtles

By Scott Aker
Special to The Washington Post
Thursday, July 30, 2009

Q We planted a Crimson Cloud hawthorn six years ago. In the spring it produces a wealth of healthy-looking leaves but hardly any flowers. By early summer the leaves have turned yellow-brown and begin to drop. By the end of August it looks dead. The tree starts bravely again the next spring. What is the problem, and what can we do about it?

A Your hawthorn tree is probably suffering from entomosporium leaf spot. Crimson Cloud is one of the most susceptible hawthorn varieties for this, along with Paulii. If you want to keep the foliage in good condition, you will have to spray it with a fungicide. Begin to spray the tree at bud break and continue throughout the growing season as long as wet weather is prevalent.

Several fungicides are suitable, but sprays containing myclobutanil require less-frequent application, at two- to three-week intervals. Most other fungicides should be applied every two weeks.

If you don't want to spray the tree, consider replacing it with a resistant hawthorn such as Winter King. The flowers are white instead of pink, but you will have attractive and persistent fruits much of the winter and much better foliage throughout the summer.

If you need a small tree with pink flowers in spring, choose an Okame flowering cherry or pink flowering dogwood.

I live in a condo that has huge crape myrtles along the fence of my patio property. They need pruning by a professional with knowledge. Can you recommend an arborist, both for these trees and others needing attention? Landscapers so far have been inadequate.

Why do you think the trees need pruning? Crape myrtles are at their best if pruned sparingly. Although they can recover from drastic pruning or dieback from a particularly severe winter, they develop their best branch structure if allowed to grow naturally over time.

Many people plant crape myrtles without realizing their ultimate size, which may be as much as 25 feet tall with a similar spread. Pruning to keep crape myrtles within a certain space does not work well because of their ability to grow rapidly and vigorously afterward. Some people prune them each year in spring when new growth commences. This unfortunate practice causes rank growth and oversize flower heads that tend to bend over when laden with rain.

If the fence line needs something that functions more as a shrub, you may want to contact your condo board and ask for replacements that won't need to be pruned. Tonto, Hopi and Caddo are first-rate crape myrtle varieties that don't get much taller than 10 feet.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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