Allen D. Owings | 6/6/2008 6:42:17 PM
The LSU AgCenter has conducted a considerable amount of evaluation research on crape myrtles over the last 10-plus years, according to LSU AgCenter horticulturist Dr. Allen Owings.
“Probably 40-50 varieties are worthy of being grown and sold in Louisiana,” Owing says. Garden centers have anywhere from 10-20 varieties available during the late spring and early summer months.
Owings favorites are Natchez, Muskogee and Tuscarora among the large crape myrtles. He likes Acoma, Sioux and Tonto for the intermediate (also called semi-dwarf) varieties.
“Natchez is the top-performing crape myrtle in the southeastern United States,” Owings says, noting it was introduced by the U.S. National Arboretum in 1978. White flowers and exfoliating bark are characteristic of this variety that reaches heights of 30 feet at maturity. Bloom period is about 110 days in Louisiana, starting in early June. It has very large blooms.
Muskogee was introduced in 1978 and has medium-size, light-lavender flowers. Blooming period is excellent, beginning in mid-June and lasting 110-120 days. It has good tolerance to powdery mildew and leaf spot. Exfoliating bark is grayish tan, tan or medium brown. The bark of this variety exfoliates but not as much so as Natchez and Tuscarora. It reaches a mature height of more than 20 feet.
Tuscarora was introduced in 1981 and is noted for its coral pink flowers. It is less susceptible than most varieties to powdery mildew and leaf spot. Flowering begins in late June or early July and continues for 70-80 days. The trunk has mottled, light-brown bark that exfoliates increasingly as the tree ages. It easily reaches heights of 25 feet in the landscape and has performed well across Louisiana.
Tonto is a semi-dwarf to medium crape myrtle, reaching heights of 12-14 feet. It was released by the U.S. National Arboretum in 1990 and has been recognized as a Georgia Gold Medal winner in 1996 and Mississippi Medallion plant in 1999. It has excellent resistance to leaf spot and powdery mildew. It retains its foliage into the fall. It displays deep-red flowers and has good exfoliating bark.
Acoma also was introduced by the U.S. National Arboretum and reaches a height of 10-14 feet. It is similar in size to Tonto. It has a weeping or cascading growth habit. White flowers appear in mid- to late June and last around 90 days. Its powdery mildew resistance is good. In some years, leaf spot can be found. Defoliation is not a problem. Its light-gray bark exfoliates as the plant nears maturity. It has good cold hardiness.
Sioux was recognized as a Georgia Gold Medal winner in 1996 and a Mississippi Medallion plant in1999. It was found to have good powdery mildew resistance in LSU AgCenter trials. It has some susceptibility to leaf spot. Its flowers are vivid pink and last from June through September. Mature height ranges from 10-15 feet but can vary widely.
Keys to success with crape myrtles include adequate sunlight, ideal soil pH, drainage, proper pruning, regular fertilization, proper mulching and insect control.
Crape myrtles need full sun to perform the best, grow the best and bloom the best. This means eight hours or more of direct sun daily. Many of us underestimate the amount the amount of sun that our landscapes receive. Check sun patterns in the morning, during the middle of the day and during late afternoon.
Soil pH is important for crape myrtles, but maybe not as important as it is for some of our other landscape plants. Crape myrtles like a soil pH of 6.0-6.5. This is considered slightly acid. Do not guess on soil pH – soil test. Lower pH with sulfur products and raise pH with lime products, but always do this based on the results of a soil sample.
What about pruning? We are not in the right time of the year for crape myrtle pruning, Owings says, noting that February is the right month for that. Prune these trees to maintain a natural shape. Thin out branches; do not top or just “hack off the tops.”
Fertilization is very important. This is especially true if you are not following other crape myrtle cultural practices and care. To maximize spring growth and the resultant summer bloom, fertilize crape myrtles in early spring just prior to new growth. A fertilizer like 8-8-8 or 13-13-13 will work fine and is recommended for crape myrtles.
It is best to place fertilizer in drilled holes in the ground about 8 inches deep rather than simply throwing it on top of the ground. You can fertilize later in the spring and in the summer but the benefit to the plants is not as good as a late winter or early spring application, Owings says.
Mulching is, unfortunately, incorrectly done in many residential and commercial landscape plantings these days, Owings says. Go out with mulch instead of up with it.
“Many times now you will see mulch piled around the base of trees,” Owings says, warning, “Do not do this.” Instead, spread mulch out toward the end of the branches and mulch with pine straw, pine bark or wood chips to a depth of 2-3 inches. Refresh the layer as needed. Keep mulch off the stem and lower trunk areas of the trees.
One frequent crape myrtle problem is insect damage.
“Actually, insects do not do that much damage to the trees, but aphids feeding on the new shoot growth in the spring can be a problem,” Owings clarifies. White flies can be a problem, too. Left unchecked, these insects will release their bodily fluids onto the foliage. Their “honeydew” leads to sooty mold, the black discoloration that occurs normally in the early summer through fall months. If you control the insects, no sooty mold will develop.
For related gardening and landscape information, click on the Lawn and Garden link at the LSU AgCenter Web site, www.lsuagcenter.com. Also, contact the county agent in your local parish LSU AgCenter office.