It's always enjoyable when I get to answer your questions.
QCan you save my black-eyed Susans (Rudbeckia fulgida Goldsturm), descendants of six plants installed 20 years ago? I noticed a disease on them in 2001 and it is now affecting plants throughout my yard. It starts as brown, dry patches or spots on leaves and stems. Eventually the entire leaf turns brown or black. Sometimes the plant turns black and shrivels to the ground. Flowers are smaller, some with irregular petals. The plants are shorter than usual. -- Judy Harbeck
AI believe you are seeing a form of anthracnose. Keep soil free of dead leaves and other debris. Open the area to air circulation. These plants generally prefer full sun and well-drained soil, with good air circulation.
Anthracnose on perennials can wreak havoc for several years, and then plants can return to vigor. If your plantings are making it through the season and flowering now, try to coax a healthy stand next year using a dormant soil application of a lime-sulfur fungicide before the leaves emerge in spring to keep the spores from growing. It is a mineral-based soil fungicide that is administered as a spray. Don't use a sprayer that has been used for herbicide. Follow all directions.
I wonder if wildflowers are possible in my back yard adjacent to Rock Creek in Olney. We have lots of deer and I don't want to go to the trouble and expense just to provide them with a smorgasbord. -- Beth Lewis
Wildflowers are certainly possible in a sunny area. Deer can browse here and there on wildflowers with almost no noticeable damage.
We cut down three large white pine trees and ground their stumps. When can we replant at this site? Must we replenish the soil? -- Delores Petzold
Remove the wood chips from the stump grinding. Replace with topsoil mixed with about one-quarter to one-third compost. You can plant another tree in that area right away if the soil is dry. Place the root ball of the new tree about 25 percent higher than the existing soil line and cover only to the top of the root ball with soil.
Why shouldn't boxwoods be mulched? -- Quintin C. McClellan
Boxwoods are susceptible to a variety of fungi. Encouraging air circulation and drainage (not holding excess moisture) around the roots, as well as keeping soil clean of debris, are good ways to discourage fungal spores. The other reason not to mulch, according to Ethel Dutky, plant pathologist at the University of Maryland, is because voles love boxwood roots. This tiny rodent burrows through the easiest medium to reach roots. Therefore, mulch under boxwoods offers the path of least resistance for voles to reach the roots.
When and how should I prune my two-year-old little gem magnolia? -- Peter Hooper
Treat it like a shrub, in that it can be selectively pruned back to a leaf or juncture with another branch. Don't prune off the lower limbs, and let the plant grow slightly wider at the bottom than the top to maintain the lower foliage. Prune it for shape after winter, reaching inside to cut one branch at a time. Assess the shape after each cut. If it flowers -- little gem is not profuse, but beautifully scented -- shape it in the spring or after flowering.
Mosquitoes make it almost impossible to be outside in the summer, day or night. Is there an environmentally safe mosquito control spray? My husband and I tried a Mosquito Magnet, but it did not do a very good job. -- Gerrie Wetzel
Here are ways you can address the problem:
Insect repellents are probably the best defense against mosquitoes. Reportedly, the longest-lasting repellent contains Deet. There are less toxic repellents to apply to our skin, such as Skin-So-Soft and Green Ban, that need to be applied more often to have the same value. Smoke repels mosquitoes too. It can be in the form of yard torches and citronella table candles. If you have window or porch screens, make sure they are secure and not torn.
Dump standing water if you see it in buckets, pots or other water holding devices. Don't let puddles form on your property. Keep the rain gutters clean. If you have a water garden, fish love mosquito larvae. Where there are no fish, float a product containing bacteria called Bt that kill mosquito larvae. It's sold commercially as Mosquito Dunks. The larvae live in still water, so aerate with a pump.
As much as I am against spraying insecticide, if there is a good chance that we will contract a dreaded disease, it's an option. Mosquitoes are vectors for eastern equine encephalitis, West Nile virus, St. Louis encephalitis, malaria and dog heartworm. Remember, when you fog the area, it's with poison. Use pyrethrum; it's all natural, biodegrades quickly and has a short-term effect. You could spray for an upcoming event, but it will kill the bees and butterflies too.
I cannot decide between a flowering crab apple that will stay within a 12-foot-wide space and a small deciduous magnolia. Every reference I check to determine the spread of these trees is different. -- Kirsten Roddy
Tree sizes are certainly not an exact science. I recommend the crab apple hybrid "Sugar Tyme" because of its exceptional disease resistance and extra ornamental value from the large numbers of small crab apples that look like berries as they ripen and persist on the tree through winter. It is listed as a 15-foot spread, probably in 15 to 20 years. A magnolia that stays small, flowers pink and blooms later than the other star magnolias is a hybrid called "Waterlily" that has about a 10-foot spread.
Our driveway is two concrete strips with an 18-inch wide grass strip down the middle. What plants or other treatments would you recommend for the strip? The driveway is long, and we have sections that get a great deal of sun while others remain in shade. -- Cindy Donn
If the strips are not compacted by tires or covered by vehicles during daylight, low-growing, spreading materials can work. Try mazus (M. reptans), creeping Jenny (Lysimachia nummularia), bugleweed (Ajuga reptans) and wild or European ginger (Asarum species). Till and amend the soil with about 25 percent compost. Install plant groupings of the same species for a tapestry effect. Repeat plants that do well. Keep the plants moist as they establish, then your job will be to keep them contained between the concrete strips over the years.
Can wisteria be aggressively renewal pruned? -- Andrew Mytelka
Wisteria must be renewal pruned regularly. It is a vigorous plant that will wrap around anything it contacts. Prune it as a vine, training it to grow onto a strong trellis, set firmly in the ground. Between now and the end of the month, cut back the long runners that grew early in the season, to control the growth. In fall, prune new shoots and finger-thick woody stems back to short stubs, leaving the bottom three to four spur-shaped buds on these stems. They produce fragrant large racemes of flowers, usually from lower buds, in spring. Wisteria sometimes alternates between good and poor blooming years.
We do not want our pyracantha to grow to a such height that it blocks windows. When is it best to prune? Last year we trimmed it and it didn't produce berries in the fall. The plants are located in a well-drained area, directly in front of the house. -- Carl and Mary Winterwerp
Pyracantha should be pruned before growth begins in spring. These plants do not like severe pruning. Cut stems to vigorous growing younger wood. Leaving a stub with no leaf or branch just below the cut will often result in a dead branch. New growth can be pinched to increase flowers and berries. The main shape of the plant can be controlled by leaving the branches to grow where you want them and pruning them where you don't want them. If you prune them too late in the season, or shear them, you sacrifice berries.
Is holly superior to leyland cypress as a screen in a residential yard? -- Bentley Andrews
I am not a champion of leyland cypress, because it loses the lower branches that you count on for screening as soon as it gets shaded by the upper limbs, and it is a weak, shallow-rooted plant that will fall over in high winds and wet soil. I often recommend Nellie R. Stevens hollies for evergreen screens because they grow quickly, reaching 15 feet by 15 feet in maturity. Shear back to any size in late winter before growth begins. I like dragon lady hollies (Ilex x aquapernyi "Dragon Lady") for narrow sites. They grow about six feet wide by 10 to 15 feet tall.
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.