Fall is here and many of your gardening questions relate to autumn plant care and cultural requirements of plants you've watched grow all year. Here are some answers:
Q I was shocked to read your Oct. 22 column recommending winged euonymus (Euonymus alatus) for its fall color. You did say the plant is falling out of favor because of its invasive characteristics. Can you provide more information on this plant, since the Virginia Department of Conservation and Recreation is recommending that homeowners do not install it? -- Susan Clark
A The Asian native winged euonymus, often known as burning bush, elbowed its way into the natural environment rather quickly. I am open-minded when it comes to giving an introduced plant a chance in our climate. Unfortunately, this euonymus is one of numerous introduced invasive plants that are competing for space with natives. Some of these native plants provide vital habitats for wildlife, which can be forced to leave or perish if they can't co-exist with the invasive plant. Fortunately, wildlife seems to have accepted this large, exceptionally shade-tolerant shrub. In "Attracting Birds to Your Backyard," Sally Roth writes, "birds relish the seeds and many birds use it (burning bush euonymus) for nest sites and shelter." These facts can make it a useful plant.
That said, trying to keep this plant from invading our forests is an excellent cause. We can begin to weed out and saw down those we have control over but enjoy the fall color, and urge readers and wildlife admirers to do the same, while encouraging them to help control its spread.
Do you know of any problems with using stainless steel screws to attach lights to trees? -- Constantine G. Pergantis
No -- in fact, using stainless steel screws to attach lights or other ornaments to trees is superior to other methods of installation. Do not attach lights with straps. They will girdle a trunk and, if left on the tree, will kill it by cutting off the flow of nutrients from the roots to the canopy. On the other hand, drilling or screwing into a tree affects only the small area where the screws penetrate. The tree will grow around that, and all other parts of the trunk are unaffected.
Make sure the screws hold the fixture and wire a quarter-inch to half-inch away from the tree; check them every couple of years for adjustment to maintain that distance. This ensures that the tree won't grow into the fixtures and wires.
I need advice on a trumpet vine. It is sending shoots up all over my garden, into the lawn and under the deck. We've tried putting Roundup on the vine and digging it up but have not been successful in eradicating it. Do you have any suggestions? -- Sherry Bell
Trumpet vine (Campsis radicans) is a beautiful, flowering, hummingbird-attracting native but is an aggressive vine. I've eradicated it with glyphosate (Roundup or Kleeraway).
Cut the stems back and pull what you can. Look for regrowth in spring. Seedlings are easy to find because of distinctive deeply serrated margins on leaflets. Spray new growth when it has at least six leaves, before it climbs onto other plants. Apply herbicide carefully, following all labeled instructions, and be patient. It takes about five to 10 days before you see results, but it will kill roots and top growth. Trumpet creeper is tough enough that a second application might be needed.
If you want to train your vine, use a strong support, such as a wall, deck or fence post. Pull seedlings. Keep shoots growing from the parent plant from reaching the ground. They will root and spread quickly. Prune all stems not firmly attached to a support. Remove fading flowers before they form seeds. Plant this vine in the poorest soils where nothing else will grow.
We have a beautiful horse chestnut on our front lawn. I am concerned about its loss of leaves early and quickly starting in early September. The leaves turn brown, shrivel up quickly and fall. Can that be corrected? I would like to do whatever I can to save and protect this tree. We live in Toronto, Ontario. -- Shani Rogers
The problem you are describing is typical for horse chestnuts (Aesculus hippocastanum). In the mid-Atlantic states and other areas that have hot summers with humidity, they are one of the first trees to defoliate in fall. The reason is often leaf scorch, which usually causes them to brown and lose their leaves by late summer or early fall. They are susceptible to numerous diseases for which control is difficult, so treating can be futile. Early leaf drop might eventually stress your tree, and opportunistic insects and diseases, like scale, borer, bagworm, leaf blotch, powdery mildew and anthracnose, can infest and infect the tree. These are not worth treating, and the tree will continue to leaf out in spring. After many years, your tree might decline, but because of its showy May flowers, the shade it offers and interesting foliage, it is worth enjoying while you have it. You might try planting a red buckeye (Aesculus pavia). It's smaller (10 to 20 feet), longer-lived, tolerant of partial shade, and much less susceptible to diseases and insects.
We have crape myrtle trees and hydrangeas in our back yard. I was advised to cut the hydrangea to about a foot from the root and trim back the crape myrtles, including the top branches. Is now the proper time? Are these correct pruning practices? -- Annette Baratta
This is not the time. Some hydrangeas, like tardiva (Hydrangea paniculata Tardiva), flower white on the same year's stems in late summer or early fall and can be cut to 12 inches around March 1, before growth begins in spring. The more common hydrangeas in this area are bigleaf hydrangeas (H. macropylla) that usually have pink or blue ball-shaped flowers and bloom on the previous year's growth, so they must not be pruned until after blooming in June, to produce flower buds for the following year.
To prune your crape myrtle trees, wait until new growth emerges in spring. Never cut the top branches into an even, straight line unless you are maintaining a formally pruned topiary. It's bad for all trees and promotes weak wood and excess sucker growth. Cut only dead branches and inside and crossing wood that will grow into each other. If your crape myrtles have multiple stems, try to keep them to a clump of three to five trunks. Prune the suckers that grow from the base of the plant, and as the tree grows taller, keep the lowest limbs at least six feet above ground level. In this way the tree will display its handsome bark and serve as a small flowering tree over your garden all summer -- provided it is growing in full sun.
I live in upstate New York. This year, I grew seven urns of lavender. I don't want to lose the plants. Can I bring them in for the winter? -- Lynne Agnew
If you want lavender to live over winter in areas of heavy frost, such as upstate New York, grow it in a container and bring it into a sunny room that will stay about 40 to 60 degrees Fahrenheit. A potting mix that is high in sand and has a layer of gravel in the bottom of the pot is the best growing medium. Closely monitor the moisture in the container. It dare not get too wet, and foliage should not be allowed to get dry and crumbly.
In the Washington region, we can grow lavender outdoors. It is a low-growing woody shrub that does best in exceptionally well-drained conditions. Constant moisture or hard frosts (below minus 5 degrees Fahrenheit) will kill this plant. Install in spring near a sunny wall, and prune about one-third to half of the top growth in summer after flowering or in fall, but well before any chance of frost. Pruning in spring will reduce its flowering. Trim once a year. And, of course, clip flowers whenever you want to use them for their fragrance or distinctive taste in candies or cookies.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, www.gardenlerner.com.