My house is very close to the road. What evergreen shrubs can I plant beneath the canopy of trees in my front yard to act as a screen and muffle traffic noise?
A. J. George, via email
Suzanne Edney, a landscape designer in Apex, North Carolina, replies: The most effective way to block out traffic noise on heavily travelled roads is with a screen of small trees or shrubs. Rhododendron species, Lonicera fragrantissima, Chamaecyparis obtusa, Kalmia species, Myrica species, Euonymous japonica, Illicium floridanum, and Tsuga canadensis all are suitable plants for screening in shady locations in USDA Hardiness Zones 5 through 7. Although these shrubs tolerate dense shade, they will thrive in shade dappled with filtered sunlight. Therefore, thin the canopy of your trees to allow more light to reach the ground and more air to circulate. Plant a mix of three to five different types of shrubs to avoid losing the entire planting to a pest or disease specific to one plant.
Root competition for water and nutrients from established trees poses a direct threat to the vitality and longevity of understory shrub plantings. To avoid this problem, plant the shrubs in a 12-inches-tall by 3-to-5-feet-wide berm made up of a soil mixture similar to your native soil. Shrubs planted in the berm will develop a more continuous root run, and will fill in faster to form a screen. Wind the berm like a ribbon through the established trees, keeping away from the tree trunks of the existing canopy, and covering no more than 25 percent of the existing tree roots to avoid smothering them.
An alternative plan is to erect a solid, sound-blocking fence, and cover it with a hardy ivy such as Hedera ‘Bulgaria’ or H. ‘Hebron’ for a green look. Or alternate the fencing with bermed shrub plantings by filling the first 20 feet with shrubs, the next 10 feet with fencing, and so on. Repeat the combination until the length of property is covered.