Your questions this week lead me to believe you are standing in line for answers that will send you running to the garden.
QWhen should I prune my wisteria? It is mature but had no flowers last year. -- Can Sarratt
AOur wisteria didn't flower well last year. They tend to alternate years, one heavy and the next light. It can take decades for some seed-grown wisteria to flower at all, but as long as yours bloomed in previous years, it will again.
My preference is to prune wisteria in July after it flowers. Cut the long, wavy stems back to about eight inches (about six buds) long. Then, in late winter or early spring, prune the same stems back to three buds, or about four inches long. A free-flowering wisteria will bloom with no pruning, so a major reason to cut it back is to control its unruly growth.
What's the proper care for a night-blooming cereus? -- Janet Riley
Night-blooming cereus (Selenicereus grandiflorus) requires temperatures of more than 59 degrees Fahrenheit in sun or partial shade, with exceptionally well-drained soil that contains some leaf mold and sand. In colder temperatures, grow it in a greenhouse. To ensure drainage, plant in a growth medium for epiphytic cacti, or use another cactus mix available at your garden center. Use no fertilizer and keep it barely moist in winter. Water it freely and fertilize with a water-soluble fertilizer at half the recommended rate, once a month, when actively growing.
We have five- to six-foot yews. Can I prune them back to two feet and do it during this unusually cold winter? -- Mary Lawrence
You can prune yews to two feet and they will grow back the same season 99 percent of the time. Leave half to two-thirds of the foliage until next year. New growth will cover old cuts. Prune the rest of the old growth next year. Yews should not be pruned wet. Try to make your major cuts by mid-March.
I worry that trying to remove snow from the top of our shrubs may break brittle branches. What should I do? -- Liz Cook
Brush off the light stuff. Trying to peel or shovel off the icy cover will do more harm than good. Just let it melt naturally.
How many years can I grow tomato plants in the same soil? -- Bebe Olsen
Crop rotation combats fungi. Generally, the theory is to plant tomatoes one year; feed soil heavily with fresh compost and fish meal, fish emulsion or another sea-based product the following spring; and then plant cabbage. After that year, plant cucurbits such as cucumbers, pumpkins, gourds, melons and squash. The fourth season, install parsley-family plants such as celery, coriander, cumin, parsnip, parsley and carrots. Then go back to tomatoes the next year.
I have two white crape myrtles about 30 feet from the house. I don't want to let them get too tall. Some books say to avoid topping them. Advice? -- Chet Griffin
Do not top them. When you cut off the top of any tree it causes many weaker stems to grow where a strong branch once grew. The form is better and the tree is more resistant to disease and insects if you do not top it.
I have two old boxwood shrubs that dwarf the front of my house. I want to cut them down to a rectangular shape and reduce their size by half. With this harsh winter, can I wait a week or two to prune? -- Barbara Kott
You can prune boxwoods hard, and they will grow back through bare stems. They take about three years for foliage to renew, so cut them down over a three-year period. Pruning them into rectangles will take three to five years, gradually cutting out the largest, oldest wood to make openings. The first year, cut a third of the old wood. The second, cut another third of the old growth, and cut the rest the third year. Then the shrub will need to grow enough new stems and leaves that you can begin to shape the boxwood into a rectangle. The boxwood would be healthier if the shrub could grow back to take on its natural shape but be kept smaller. With this harsh weather, wait until the middle of March to do your pruning.
We installed pink coreopsis. They grew into two-foot-wide shrubs but never flowered. The following spring and summer, the same thing happened, so we did not cut them back. Now they are looking a bit scraggly, with lots of brown areas. What's the right way to manage them? -- Fran and Ken Finkelstein
Coreopsis are free-flowering perennials in full sun. If they don't get at least seven hours of sunlight, they will grow foliage but produce no flowers. They should be cut back annually but will regrow from their roots whether you cut them back or not. At the rate this winter is going, spring cleanup might be your first chance to get to them. Give them a couple of growing seasons to begin to make a show.
I have three camellia bushes. Do I prune them in late winter or early fall? They bloom in April. -- Barbara Cotter
The camellias I have seen this month appear to have wintered all right and will probably bloom quite well. The time to prune your camellias is right after they flower in April. Do light, corrective pruning, and cut off winter damage.
A few years ago I planted a buckeye seedling on the southeast side of my house with less-than-optimum sun. Two years ago I transplanted it about six feet from the house into more sun. The plant has grown six to 12 inches a year, develops beautiful oval leaves and red flowers, and forms buds for the next year, but it goes dormant around mid-July. What can I do to extend its growing cycle? -- Vic Cohen
Ohio buckeye (Aesculus glabra), the state tree of Ohio and native from Pennsylvania to Nebraska, does not like our climate. Its main complaint is the warm summer. It defoliates by July or August every year. It is drought tolerant but can use a little shade from our hot afternoon sun. If the tree is six feet from the wall of your house, it is way too close. Transplant it at least 12 to 15 feet away.
Would it be okay to prune several pyracantha, six feet tall, 20 years old? And if so, how far back should they be pruned? -- Bonnie Tyler
Older pyracantha often doesn't respond well to hard pruning. Try to leave some greenery on it to aid in the renewal process. Don't prune when wet; it is susceptible to many diseases that can be spread that way. At six feet and 20 years old, the plant sounds as if it has been pruned successfully in the past. Don't shear it. Prune selectively, standing back to look at the shape every several cuts. Prune the biggest, oldest wood to crossing branches or leaves as you shape and make it smaller. It should be done in late winter, but this year wait until growth begins in late March or April.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. His e-mail address is email@example.com; his Web page is at www.gardenlerner.com.