Texas bluebells are good wildflowers for the garden, too
Q: I ordered some lisianthus, Texas bluebells. Should I give them full sun? What soil would they like?
Texas bluebells, Eustoma exaltatum, are native wildflowers with tulip-shaped blooms that appear late spring through summer. They’re best in sun or part sun and a moist, well-draining soil.
Texas bluebells also are known as prairie gentian and lisianthus. Japanese hybridizers have created pink, white and purple-blue cultivars. The charming flowers are handsome against the blue-gray foliage and in a vase.
The plants typically are perennial in native habitats. Hybrids often are annuals.
Q: I read two articles that identified two different gardening zones for this area. One listed us in Zone 9. I had heard this before. The other listed us in Zone 8. This was new to me. Can you shed some light on this?
A: The USDA Plant Hardiness Zone Map has changed during the years I’ve been writing about gardening and indicates increasingly warmer average winter temperatures for this area. The current map is divided into 10-degree Fahrenheit zones, and each is divided into 5-degree differences labeled “a” or “b.”
The latest map, produced in 2012, lists the city of Houston and Kingwood in Zone 9a, with the average annual minimum winter temperature at 20-25 degrees Fahrenheit.
On the 2007 map, the Zone 8-9 line cut through Harris County, so that communities north of Houston were designated as Zone 8b. Currently, only a tiny northwestern tip of the county lies in Zone 8b, with average lows at 15-20 degrees. Even a good portion of Montgomery County now lies in Zone 9a.
Gardeners can type in their ZIP codes to find their zones at planthardiness.ars.usda. gov. Then, check the hardiness zone listed on the plant tag while shopping at your nursery for plants suitable for your garden.
Q: Do you know of a dwarf loropetalum variety that would do well in Houston? Jean Winkelman, Houston
A: I have tried a few dwarf loropetalums and had so-so results. I suspect the shrubs would show stronger, denser growth if I moved them to a bed with better drainage and slightly more acidic soil. Every garden is different, so perhaps you’ll be pleased from the start if you try a small form of the near-indesctructible large loropetalums seen in so many local gardens.
There are dwarf lororpetalums that vary from 2-5 feet in the Southern Living Plant Collection. ‘Jazz Hands,’ a Proven Winners selection, shows promise in sun and a fertile, well-draining soil.
Q: I found a swarm of giant aphids on my crape myrtle. Are they giant bark aphids? I sprayed with vinegar, but I think I need to be more aggressive in getting rid of them. Cindy Price, League City
A: A congregation of giant bark aphids could be confused with bark lice, which are gregarious beneficials that also cluster in herds. Check online for images of these two insects to identify and decide whether you need any treatment. The giant aphid species seen in Houston typically is gray with black dots. Bark lice have yellowish bands.
Bark lice create, then live and work beneath, a protective webbing that runs along the trunk or branches. Just let the insects do their job of cleaning up your tree. The web eventually disappears.
Should you determine aphids are present, you may decide no action is needed. Or go with nontoxic or low-toxic treatments to avoid killing beneficial insects such as predatory wasps and ladybugs, which are natural enemies of aphids. Strong jets of water are effective, but it may be difficult to reach middle to upper regions of the tree. Repeated action is usually required.
Insecticidal soap and horticultural oil also work.