Photo courtesy of the U. S. National Arboretum.
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 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. Also, [Louisiana residents] contact the county agent in your local parish LSU AgCenter office.