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The Garden Plot for February 02, 2007
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: "Energy Efficient Plants"
Plants can make your home more energy efficient. Carefully placed trees and shrubs can help to cool and retain heat in homes. Unprotected homes loose more heat on a cold windy day than on a cold, still day. So, planting windbreaks can reduce winter fuel consumption. In one South Dakota study, a windbreak reduced winter energy use by 34%. Windbreaks should be planted perpendicular to the prevailing wind, and located upwind from your house. If possible, plant windbreaks 40 to 50 feet upwind of a single story house and choose species that will reach a height of 15 feet. Trees can be planted in 2 to 3 rows with approximately 6’ between each tree. For example, row one could be an evergreen shrub, such as juniper, followed by row two, consisting of taller evergreen trees, such as spruce or pine. Thick, deciduous shrub windbreaks can also be effective. The north side of my house is protected by a dense 15 feet high shrub row I call “the great wall of lilac”. The trick is to let the lilac fill in and only prune to maintain height. If you don’t have much room, even fences with draping vines can provide some windbreak.
Individual trees and shrubs, planted close to buildings, reduce wind currents that chill outside wall surfaces. These foundation plantings create dead air space that helps to slow heat loss from buildings. In summer, the same dead air space helps to insulate homes from hot, outside air. Evergreen shrubs and trees are most effective because they are often thicker and bushier in the winter. But, shrub roses, lilac, mockorange, Oakleaf sumac and potentilla also provide a tight barrier against air movement if planted close together. Any woody planting surrounding the house will slow the escape of heat, but the thicker and bushier the plant, the more insulating effect you will gain.
Before the advent of air conditioning, it was common to plant for summer shade. Most older homes have deciduous shade trees strategically located along their sunny, south sides. These deciduous trees shade the summer sun, but still maximize winter sunlight because they shed their leaves in the fall, and let the sun’s rays warm south-facing walls and windows on sunny winter days. Tall, deciduous shrubs provide summer shading as well. Ten years ago I began to encourage the growth of suckers from two aspen trees planted on the south side of my house. Now I have an aspen grove consisting of approximately 40 3-4 inch diameter 20 feet high aspen. This aspen grove provides deep shade for my south-facing sun room in the summer. But now, in February, the leafless aspen allow so little shade that my unheated sunroom was a balmy 75 F during the recent sunny spell we enjoyed.
Besides planting deciduous trees and shrubs to shade south-facing windows and walls, you can also help to cool your home by planting vegetation on east and west-facing walls. Use deciduous or evergreen shrubs, small trees, or arbored vines that reach a height great enough to cover the height of your walls. To maximize summer cooling, you may also want to make sure south-facing roof surfaces have shade in the summer. Choose taller, deciduous trees with overhanging crowns, such as maple, white ash, and hackberry. Since these trees need to hang over the roof to provide summer cooling, do not choose weak-wooded trees, such as Siberian elm or cottonwood, to plant this close to your home.
A well-planned landscape is not only beautiful; it can reduce year-round energy bills. For energy efficient landscapes, design to maximize winter sun, shade summer sun, and block winter winds. For more information contact your local county extension office.
Helen Atthowe's new short program of gardening tips
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