Last week's question about a fungus-prone, nonblooming crape myrtle prompted a detailed response from another master gardener with plenty of experience growing this Sacramento favorite.
"I have grown crape myrtles for several years and, as are most who garden here in Sacramento, am aware of the beauty of a well- grown one," said Barb Mantzouranis, a certified arborist and UC master gardener.
"They do have the propensity to become problematic in a few areas, but are generally very easy to care for. As an arborist as well as a master gardener, I would like to add my 2 cents on this issue.
"The article was unclear as to the type of 'fungal growth' the tree is infested with, but I would wager to guess that it would be either (or both) powdery mildew, or the fungus that grows on the excrement of scale or aphids, since both these maladies are common on this tree.
"Certainly, spraying is an option, but I feel there are least-toxic measures that can be tried first," added Mantzouranis. "My success rate thus far has resulted in my not needing to use chemicals in my garden for well over 20 years."
Powdery mildew is carried to plants via wind, not water, she explained. That allows water to be used in mildew's control.
"Use blasts of water to wash the mildew off the foliage of infected plants," she said. "This should be done early in the morning so that foliage has a chance to dry before the sun goes down, as wet foliage after sundown, coupled with the drop in temperature overnight, actually encourages and furthers the growth of mildew.
"As far as any other fungi that may be present on the leaves and stems, the plant should be checked for scale and aphids," Mantzouranis continued. "Keeping the plants free of ants with Tanglefoot (a sticky substance that traps ants) applied at the base (of the tree) is most beneficial in this respect, as it restricts the 'herding' of the scales and aphids that ants are so notorious for.
"Also, the strong spray of the hose while cleaning the leaves of the tree for removal of powdery mildew is certainly a good way to keep the pest population at bay," she added.
What about pruning?
"These trees need a good pruning each year to produce flowers. I prune a good 18 inches off the outermost tips of previous years' growth from my trees each winter," she said. "I reserve this pruning to late February or early March, as the trees bloom on new wood, and pruning at that time ensures a good amount of new growth."
Younger trees need less pruning, she noted.
"My trees are pretty mature, and it sounds like the tree mentioned in the article is quite young, so 18 inches would be far too much. When my trees were very young, I took about a third of the previous year's growth off at the ends of the branches to encourage good new wood growth, which in turn ensured good flowering.
"In addition, I am careful to keep the plant pruned so that good air circulation is maintained, especially on the interior. This also helps with disease and pest prevention, as the overly shady interior of a plant is often where problems are born.
"Although these trees do resent overwatering and overfertilization, these problems generally show up in the foliage at some point, and the writer said her foliage looked healthy.
"The lack of flowering then, in my opinion, is a result of a lack of sunlight."
Crape myrtles need full sun to be at their best and at least six to eight hours a day to produce flowers.
"The old adage 'Right tree in the right place' is very important here," she said. "If this tree is not receiving the proper amount of sunlight, no amount of other care can yield results as far as blooming is concerned. These trees can thrive in the often-intense heat we experience, but that in no way can substitute for the direct sunlight they need for bloom."
Even mildew-resistant varieties of crape myrtle can contract mildew if not planted in a sunny location and given the right care.
"These plants are not disease-proof," she noted. "If the tree is not receiving the needed amount of sunlight, then next winter while dormant and still young, the tree can be moved once more to a sunnier location."
Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.
Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to email@example.com. Please put "Garden Detective" in the subject field and include your postal address.
To read past Garden Detectives, go to http://www.sacbee.com/gardendetective
To contact your UC Extension directly, call:
Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays
Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email ceamador.ucdavis.edu
Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays
El Dorado: (530) 621-5512; 9 a.m.-noon weekdays
Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays, or leave a message and calls will be returned
Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message
Shasta, Tehama, Trinity: (530) 225-4605
Solano: (707) 784-1322; leave a message and calls will be returned
Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays
Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned