Helping Nature Help You

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By Joel M. Lerner
Saturday, August 9, 2008

A well-researched landscape design can go a long way toward lowering energy costs and putting homegrown food on the table. Nature has given us the tools to save money while being environmentally conscious.

Focus on alleviating or harnessing the power of the sun. Your house should be shielded from the heat of direct sunlight in summer, while the sun shines on plants such as vegetable gardens. When deciduous trees that provide shade in summer lose their leaves in fall, sunlight can warm the house.

Tracking the sun and the prevailing winds on your property throughout the year provides information that will help you design according to plants' needs. Then plantings can offer aesthetics, energy efficiency and food. The best designs use trees, shrubs, vines, annuals and perennials.

Trees are interesting, low-maintenance and a naturally effective overhead element, an important part of the energy-efficiency formula. When planted properly, they provide comfort, conserve energy and cut fuel costs. Properly placed shade trees can reduce summer cooling bills by 25 percent and provide a canopy to define your property.

Afternoon is the hottest time of day, with the sun in the southwestern sky. To cut air-conditioning costs, deciduous trees should be planted to shade your house during this time.

Plant trees to shade the walls, not just the roof. Roofs in today's homes are well insulated, and most of your air conditioning is lost through windows and walls. So place trees on the southern, southwestern and western sides of your house.

In winter, keep the southern, southwestern and western sides free of obstacles that might block radiant heat from reaching walls and windows. Don't use evergreen trees because they will block the winter sun. Install sturdy oaks, ashes or lindens. Plant trees about 20 to 25 feet from the house and at least 25 feet from each other. It depends on the mature size of the tree you choose.

You can also shade your air-conditioning unit or heat pump to conserve energy. According to the American Nursery and Landscape Association, shading an air-conditioning unit can ease strain on the compressor and lengthen its life. By shading heat pumps, you can save up to 3 percent on energy. Plant a flowering tree or shrub near the unit, taking care not to block air circulation. Service personnel can provide proper clearance information so you can allow your heat pump to remain correctly ventilated. Build a trellis a few feet away from the unit to grow a Montana or sweetautumn clematis ( C. montana or maximowicziana) or other vine for shade.

Deciduous vines on trellises will also give shade to south- and west-facing walls. Do not use evergreen vines. They won't allow the sun to warm the walls as well in winter.

Vines that lose their leaves can serve a function similar to that of deciduous trees. While not nearly as effective, they grow more quickly. In as little as five years, some vines, such as trumpet creeper ( Campsis radicans), five-leaf akebia and Boston ivy ( Parthenocissus tricuspidata), will grow large enough to shade a portion of your house. Plant vines so they climb on the southern and western walls of a brick or masonry house. On wooden houses, train vines on trellises next to walls to prevent decay from vines holding too much moisture.

Insulate with evergreens. Dense plantings of evergreen shrubs will provide insulation against cold air by creating a dead-air zone adjacent to the external walls. This can reduce the infiltration of cold air through walls. Plant shrubs on the northwest- and north-facing walls. These are the dominant directions winter winds blow from in the Washington region. Shrubs planted on this side of a house will reduce the wind, which severely robs structures of heat in winter. Shrubs will also slow the escape of warm air. In summer, shrubs insulate the walls and help keep cool air from escaping. To establish insulating plants on the north side, you must have a bright wall with no trees overhead. Install shrubs that are somewhat shade-tolerant, such as hollies, boxwoods and yews.

Confirm where winds blow across your property during the winter. If you block these winds with evergreens, you can help reduce fuel consumption even more. However, installing a wind block at your property line can be a challenge.

The height and density of shrubs or trees determine the amount of protection they provide. Once you determine where the winds blow across your property and against the house, block them with evergreens. Plant two or more rows. Evergreen windbreaks reduce wind velocity for a distance of about 10 times the height of the plants, so a continuous hedge 10 feet tall and 11 times that in length (110 feet) will provide protection for about 100 feet on its leeward side. Hedges installed as windbreaks can also offer a cooling effect by helping to channel the prevailing summer winds, generally blowing from the southwest in this region.

Vegetable crops will benefit from some enclosure to protect them from wildlife damage. Fences are the best enclosure. The fence should not act as a windbreak, because air circulation helps maintain healthy plants, including berry bushes, strawberries and fruit trees. Good air circulation dries foliage quickly after rain and discourages the spread of fungal diseases.

If you have the luxury of choosing the site and orientation of your house, the ideal location is midway up a southern- or southeastern-facing slope, with the longest walls and roof pitches facing slightly southeast. This allows maximum exposure to the winter sun. The most comfortable orientation for patios or other summer outdoor relaxation areas on your property is southeastern positioning with shade from the southwestern sun. A southwestern exposure will warm the front of your house when trees lose their leaves.

When designing on a hillside, remember not to block the flow of cold air. Cold or frozen air flows downhill, always seeking the lowest level. Install masses or groupings of shrubs and trees so that they allow that natural downhill flow. Prevent the creation of "cold-air lakes" near the house in the winter by designing plants along the hills, not across them. Don't build a patio or other structure in a low spot, where this frigid air collects.

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


© 2008 The Washington Post Company

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