Reliable crape myrtle flowers lagging this year

Richard Bogren, Owings, Allen D.  |  7/13/2015 11:37:58 PM

The highly reliable Natchez crape myrtle is flowering late and has fewer blooms this summer. (Photo by Allen Owings, LSU AgCenter)

Defoliation and fewer blooms occur on crape myrtles as the result of cool weather, increased rainfall and cloudy days in the spring. (Photo by Allen Owings, LSU AgCenter)

Leaf spot has been a problem on crape myrtles in Louisiana this year. (Photo by Allen Owings, LSU AgCenter)

News Release Distributed 07/13/15

HAMMOND, La. – The most popular summer-blooming tree in Louisiana is the crape myrtle with its lovely, long-lasting flowers. They generally myrtles start blooming between mid-May and early June and continue flowering for 80 to 100 days, depending on the variety.

This year, however, has seen crape myrtles blooming later and less than normal. “This is due to our cool, wet spring,” said LSU AgCenter horticulturist Allen Owings. “Cool weather in spring promotes less foliage growth, and less foliage growth in spring equates to fewer blooms in summer.”

Cool weather in spring, which occurred throughout the state this year, also slows summertime flower development. And so do cloudy days that persisted through spring.

“It has only been over the past two weeks that we’ve seen summer-like temperatures, sunny skies and drier days,” Owings said.

This year’s wet weather also resulted in large increases of Cercospora and bacterial leaf spot diseases on crape myrtles.

“We normally don’t think of this disease as having a negative impact on blooming, but the leaf spot combined with other factors this year has led to later flowering and fewer blooms – even on our best varieties,” Owings said.

Owings cited other factors that play a role in crape myrtle flowering:

– Shade. Crape myrtles require eight hours of direct sun daily to bloom well. Many times crape myrtles are planted in areas that receive four to six hours of direct sun or less – not enough for adequate bloom development.

– Variety. Some varieties don’t flower as vigorously as others. The hybrid crape myrtles usually flower first. Natchez, Tuscarora, Basham’s Party Pink and Muskogee are the earliest-flowering varieties. Semi-dwarf varieties Tonto, Acoma, Sioux and others follow a week or two later.

– Insects. Heavy infestation of aphids decreases flowering. They are the most common insect problem on crape myrtles. Whiteflies and other insects also can cause problems on crape myrtles.

– Improper pruning. Drastic pruning or pruning after new growth in the spring can delay summer flowering. Drastic pruning may promote excessive growth and less flowering.

– Too much fertilizer. Excessive fertilization, especially high amounts of nitrogen, in conjunction with other factors, primarily improper pruning, can eliminate or delay flowering.

– Wet soil. Crape myrtles need well-drained areas to grow well. Lichen growing on the bark is common on crape myrtles growing in shady areas accompanied by poorly drained soils and low levels of native soil fertility.

“Crape myrtles are still reliable landscape performers and are highly recommended,” Owings said. “The fewer flowers this year are just a result spring growing conditions around the state.”

Rick Bogren
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