Marin Master Gardeners
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Gardening with Energy Costs in Mind

May 12, 2008
Martha Proctor

 

Do you want to save energy on heating and cooling your home? Do you want to conserve fossil fuels? By employing environmentally conscious landscaping and by being selective in the choice and placement of plants, we can lower the energy costs associated with maintaining our homes. Earth Day, several days with strong winds, and the ongoing, pressing concerns regarding environmental issues bring to mind ideas as to how we could alter our gardening practices to reduce harm to the environment, save money, and have more comfortable places to live, work and play.

 

Double duty for plants and trees
Plants can significantly reduce a home’s energy needs, as it is cooler in the shade of trees and warmer behind plants that block the wind. The general rule is to plant deciduous trees on the south and west sides of a building where the sun's rays are most direct and intense. Trees such as deciduous oaks (blue, California black, red or pin oaks), elms (Chinese or American elm) or redbud (Eastern or Western redbud) trees will provide shade during summer, but permit the winter sun to provide warmth. Where there isn't room for trees, shrubs and vines can provide similar benefits. Research models by the U.S. Department of Energy predict that the proper placement of as few as three shade trees will save an average household $100-$250 in energy costs each year. For those in hotter Bay Area microclimates, a study found that air conditioning needs could be reduced by up to 75% by shading a house with trees! The cooling effect of one urban elm tree is equivalent to five air conditioning units! Extensive use of trees to shade homes, streets, driveways and large paved surfaces can cool entire communities. Studies have found summer daytime air temperatures in tree-shaded neighborhoods to be 3o to 6oF cooler than in treeless ones.
A six- to eight-foot deciduous tree planted near your home will begin shading windows the first year. Depending on the species, the tree will shade the roof in 5 to 10 years. Trees, shrubs, and groundcover plants can also shade the ground and pavement around the home. This reduces heat radiation and cools the air before it reaches your home's walls and windows. Use a large bush or row of shrubs to shade a patio or driveway. Plant a hedge to shade a sidewalk. Building a trellis for climbing vines will shade a patio area while admitting cooling breezes. Place plants in containers against a sheltered house wall but be careful not to set them in a position in which buildings create a wind tunnel. Remember, also, not to plant dense foliage immediately next to your home as this can become a haven to undesirable insects and other pests.
Wind Protection
Properly selected and placed landscaping can provide excellent wind protection and considerably reduce winter heating costs. These cost benefits will increase as the trees and shrubs mature. Although, most cold winds come from the north or west, wind direction can vary locally. Plant a dense row of evergreen trees or shrubs that have a low crown and branches low to the ground on the windy side of your home. For maximum protection and insulation, plant your windbreak slightly away from the foundation of your home at a distance equal to 2-5 times the mature height of the trees. Be careful not to plant trees too close to the south side of your home, if you want to capture warmth from the winter sun. Planting shrubs, bushes, and vines next to your house creates dead air space that insulates your home in winter and summer.
Trees, bushes, and shrubs are often planted together to force wind from the ground level to above the home. A windbreak will reduce wind speed for a distance of as much as 30 times the windbreak's height. Solid barriers, such as garden walls, will deflect the wind but may cause damaging turbulence on the leeward side of the barrier. Evergreen oaks, e.g., cork or holly oaks, Douglas fir and Cedar of Lebanon trees make great windbreaks for winter winds. Less densely branched trees are good for filtering morning sun from the east, while denser trees are better for blocking harsh afternoon summer sun. If you want to impede summer winds, choose a tree or shrub with more open branches and leaves.
The rapid air movement of strong winds can cause physical damage to plants and loss of moisture from both the foliage and the soil. Providing wind protection will slow the speed at which wind will pass a plant reducing the amount of water lost from the leaves.  And, mulching around plants reduces the wind’s drying effect on the soil.
Consider adding a roof garden, as "greenroofing," provides insulating value that further reduces heating and cooling needs. With the increased cost, both monetarily and environmentally, of using fossil fuels for heating and cooling our homes, it seems wise to consider planting a few trees in strategic places in our gardens and in our neighborhoods.

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