Even in Winter, Gardeners Have a Lot of Ground to Cover (2024)

How do you advise pruning crape myrtles? When and how much should be trimmed? -- Greig Stewart

Crape myrtles are quite flexible in the way they can be pruned. Wait until growth begins in spring to check for dead wood that must be cut. Train it as a multiple trunk tree, retaining three to five of the healthiest trunks. Cut others to ground level. As stems age, they develop beautiful exfoliating bark with tan, red and brown colors. Crape myrtles can be cut to any height to create a large shrub. When they're cut to the ground, they will sprout from the roots. They flower on current year's growth, so if sited in full sun, new stems will flower all summer into fall.

I have moss growing on my brick driveway. How can I eliminate this problem without causing any environmental damage?

-- Gilbert Bowman

Rent a power washer and spray (scour) the moss from your driveway. Commercial-quality machines do an impressive job. You can also use a scrub brush. Make this an annual garden task -- moss returns. Moss can be killed with iron sulfate, but that's in lawns. Do not be tempted to use it on paving; it can leave rust stains.

A Norway maple planted seven to eight years ago is now about 20 feet high. Grass will not grow under it. Do you have any suggestions?

-- Gus Shelcusky

The maple is shading the grass. Lawn won't grow in shade. The way to deal with areas under tree canopies is to mulch the root zone so annual planting doesn't disturb feeder roots. Mulch with a one-inch layer of compost. If the area under the canopy is so large that you want something more ornamental, plant shade-tolerant perennials. Use groupings of hellebores or rohdeas with an edging of pulmonaria. Or, plant a single species of shade-tolerant ground cover such as pachysandra, periwinkle or sweet woodruff. Keep plantings toward edge of drip line. Plant no closer than five to six feet from the trunk.

Do you have a suggestion for an effective, environmentally responsible way to reclaim an area, about 1,000 square feet, overgrown with ivy, vines and rose of Sharon? -- Leonard Taylor Jr.

Cut or mow all undesirable material to the ground. In the case of vines on trees, cut the stems at ground level and leave vines to die. When the area is cleared, you have several choices to eradicate returning vegetation.

· Cut off sunlight with landscape fabric. It is meant to cut light to the soil to keep weeds from germinating and should be left in place for a year, using soil along the edges to hold it in place.

· Cover area with clear plastic for a growing season. This will result in solarization, a method of sterilizing the soil using the heat of the sun. The heat buildup from the greenhouse effect under the plastic kills germinating seeds, funguses and insect eggs. It can take four to six weeks of intense heat. Tough weeds such as bindweed might need to be covered another year.

· Use a non-selective herbicide. To be as environmentally responsible as possible, use vinegar. White vinegar off the grocery store shelf is a 5 percent solution. Find stronger brands made for horticultural uses. Use a plastic spray bottle. Vinegar is corrosive. Glyphosate-based materials, such as Roundup or Kleeraway, are the chemical way to gain control. Apply to actively growing plants, before weeds flower and go to seed. Spray weeds in late winter, spring, summer and fall.

· Prepare soil by tilling three inches of compost into the top eight to 10 inches. Mulch area to control new encroaching weeds, while your new plantings are establishing.

I planted northern sea oats in my back yard. They spread all over the area. Is there a spray I can use to eliminate these plants without killing others growing in this space? -- Nadine G. Sparer

The grass commonly called northern sea oats (Chasmanthium latifolium) is a good example of an invasive native plant. It's a clump-forming grass, native from Pennsylvania and New Jersey across to Texas, that does well on moist sites in full sun or partial shade. This grass has interesting seed heads that self-seed prolifically. Cultivating or skimming them from the ground when they are seedlings easily controls them.

I have a pyracantha that was loaded with berries when I bought it 10 years ago. It has yet to produce one berry. It gets sun at least half the day. How can I get berries?

-- P.W. Mirras

These rose-family plants produce best in full sun, eight hours or more, but they still produce healthy foliage in some shade. If you are pruning just after flowering in May or June, the berry-producing flowers might have been removed.

We have two large dogs that have torn up the lawn in our back yard. It is fairly shady. Can you suggest something that can withstand these conditions? -- Dorothy Money

Turf won't thrive in shade, especially with the extra impact caused by compaction from two large dogs running the yard. This will keep grass from growing thick and healthy. I do not consider any low-growing plants dog-proof. Separate them with an ornamental fence pets can't jump. Pet areas can be covered with shredded bark mulch.

I heard that putting used coffee grounds around azaleas and other acid-loving plants is a good fertilizer/mulch. Are there benefits to its use? -- Jim Mongelluzzo

Coffee grounds make satisfactory mulch for all plants. They add nutrients as they break down in the soil. According to research at Purdue University, they are slightly to highly acidic and would be excellent around your azaleas.

I have a lilac, and it appears to have borers. They look white with little brown heads. How do I get rid of them? -- Julius Prezelski

You describe what the lilac borer larvae, also called ash borer, looks like. If you are seeing emergence holes in the older wood, it is likely that your diagnosis is correct. Keep borers from infesting by cutting down the trunks that have become thick (two inches or more) and are starting to show furrowed bark. Do this right after flowering. Continue to cut down the oldest lilac wood every year after flowering and your plant will stay borer-free. Lilacs renew by shoots that grow from the roots. Flower buds form on them this year and open next.

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.