Inside the Mailbag: Misbehaving Roots and a Miniature Railway

By Joel M. Lerner
Saturday, January 17, 2009

It's time to answer your garden questions again -- in winter, when time is spent out of the garden, planning what can be done to enhance it in spring.

Q: Our homeowners association will be replacing six, 20-plus-year-old locust trees that have outgrown the space they were planted in. The roots spread and are breaking up the pavement and curbs. Can you suggest trees that grow about 30 feet with roots that will grow down rather than out? -- Charlotte Barrett

A: I am presuming that the trees are honeylocusts, not true locusts. At the site where the trees and stumps are to be removed, prepare as wide an area as possible and dig deeply, about 18 inches. Mix the soil with one-third compost by volume. Good deciduous trees for this region are American hophornbeam (Ostrya virginiana) or American hornbeam (Carpinus caroliniana). Flower options are Downy serviceberry (Amelanchier arborea), kousa dogwood or American redbud.

Q: We live in a townhouse development with front yards that are five-by-eight feet or smaller. Red maples were planted by the developer, and their roots are spreading beyond the yards. How can roots be cut to avoid damage to driveways, sidewalks, foundations and lawns? -- E. Fisher

A: Do some root pruning now to remove a few surface roots. As damaged paving is replaced, cut the roots that did the lifting and pushing. Only remove what you must to protect your paving, and keep a close watch on the trees over the next several years to monitor whether they recover completely. Cut the roots with an axe or mattock at the paved areas. If you are not having any problems with moisture in your basement, the trees are not causing damage to your foundation.

Where roots are taking over lawn, yield to the tree and plant a shade garden using plumbago and late winter flowering bulbs or other tough, shade-tolerant groundcovers, such as mazus, sweet woodruff and false forget-me-not (Brunnera macrophylla). Mulch in spring with shredded bark or pine nuggets.

Q: My home faces east and has two flower beds in the front courtyard. They are filled with pea gravel six to eight inches deep. The beds get morning sun for four to five hours. Can you suggest any plants or dwarf trees that would thrive in this environment? -- Jean Busby

A: Six to eight inches of pea gravel is too deep, so remove as much as you can. Incorporate what's left deeply into the soil to create a light, well-drained and aerated medium that will be suitable for trying alpine and rock garden plants. Dwarf cryptomerias, dwarf hemlocks, daphnes, dwarf hinoki falsecypress (Chamaecyparis), bleeding hearts, bletillas, hostas and hellebores are a sampling of plants that should grow well in at least five hours of morning sun.

Q: Leaves that fall on our property don't compost in one season. They are on two acres that I have kept as a natural woodland for 28 years, except for areas close to the house. There are too many for my mulching mower to break down. Does buildup of matted leaves prevent moisture from getting to the roots of trees? Do you have any suggestions for reducing the buildup? -- Dick Dangel

A: Fallen leaves in completely natural areas will decay and promote the formation of rich soil around the base of trees and shrubs. They won't impede moisture or air from reaching the roots and will provide good moisture retention in the soil. The dense buildup is usually caused by adding to the woodland leaves that are cleaned up from landscaped areas. The combined leaves will definitely not compost in a single season without being managed. Turn the leaves for aeration and mix with greenery and some soil to break down their high carbon content.

As excess amounts are added over the years, leaves will decay more slowly. Leaves around the house and landscaped areas should be raked together and put out for collection by the county or piled and composted in a separate area. Mounds of leaves for compost will break down more quickly if you put them through a chipper/shredder before piling. Leaves that fall into the woods generally stay about six to 12 inches thick and will decay in a natural manner over time.

Q: We have a friend who has an extensive railroad system in his house and would be interested in the outdoor railway that you mentioned in a recent column. Can you give me more information about it? -- Leslie Glassberg

A: Garden railways can operate in the garden 12 months a year (especially if you have a snowplow engine), and because of exposure to the elements, you even get to conduct track inspections. "G" scale trains are the most popular type and are available in electric, steam and remote-controlled, rechargeable battery models. They can be designed and built into the landscape, running from one garden into another, or you can create a complete environment around them that includes miniature mountains, towns, alpine meadows or prairies with plants. Scaling plant material down to model railway proportion mimics nature in a diminutive manner. It's the perfect amenity for all ages to simply enjoy the garden. There are dozens of garden railway clubs. Check with your local hobby shop, or contact the Washington, Virginia & Maryland Garden Railway Society (

Q: I have been growing six ginkgos in pots for about two years. They range from 18 to 30 inches in height. Is there any way to identify the gender of the plants before transplanting them into the landscape? -- Michael S. Gray

A: Unfortunately, there is little chance that you will be able to separate males from females since it can take 20 years or more for seedling ginkgos to produce flowers.

Q: Our witch hazel has rust-colored, or dark orange, blossoms. But it does not drop leaves. They stay on well into the following spring. Can you advise? -- A. Ambre

A: You are describing the habit of a vernal witch hazel (Hamamelis vernalis). Its foliage is late to color in fall, and last year's leaves tend to persist through winter, which can detract from the ornamental value of this large shrub. However, witch hazel flowers are fragrant when they open in midwinter. If you want to see the winter flowers and can fit another witch hazel on your property, choose a hybrid with fragrant flowers on leafless stems in midwinter, such as Arnold Promise.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site,

© 2009 The Washington Post Company