Heat your home with what you plant outside

Bridget Tisthammer

Did you know that you can reduce your winter heating bill by as much as 25 percent, just by using plants?

The trick is to put the right type of plant in the right place.

There are three factors that cause heat exchange in a home: air infiltration, heat conduction and solar radiation. Air infiltration occurs when the pressure between the air outside is greater than the air inside, such as on very windy days. Cold air on the windward side (usually north or west in Colorado) pushes through tiny cracks around doors, windows and other openings in walls and ceilings. This pushes warm air outside on the leeward side (south or east). This can account for 50 percent of heat loss on the coldest, windiest days.

A good way to lower the air pressure around your home is to create an evergreen windbreak on the northwest side of your property. Distance is an important factor in the effectiveness of a windbreak. A good rule of thumb is to plant the windbreak at a distance of one to three times the trees' mature height from the house. So if the evergreens in your windbreak will reach a mature height of 20 feet, plant the trees 20 to 60 feet away from your home. This is optimal, but adequate wind protection can occur at a distance of as much as six times the trees' height.

If your space is limited, one row of a tall, narrow evergreen, such as columnar spruce, will provide adequate protection. If you have more space, plant three to five rows of different species of evergreens to provide the most wind protection. Keep a distance of 6 feet between each row. If possible, extend the row of trees 50 feet beyond the area needing protection. A two-row planting could include a row of Colorado spruce and a row of ponderosa pine. A three-row planting might include a row of junipers, as well. The mature width of the tree will determine how closely you plant. If the mature width is 20 to 30 feet, use the lower estimate of 20 feet to space your trees.

Obviously, this method takes several years of plant growth to become effective. You can obtain results more quickly by planting a thick hedge of lower-growing evergreens around the north and west foundations of your house. There are many spreading evergreens that would work well — junipers, mugo pines and dwarf spruce are just a few. This creates a space of trapped dead air, which will further insulate the walls of your home.

Heat conduction is regulated by the home's building materials, insulation R values, surface areas available for heat flow, and the difference in temperature between outside and inside surfaces of the home. Windbreaks also work to lower heat conduction in your home. In addition, they maximize the amount of solar radiation allowed into the house.

Solar radiation is the flow of sunlight through windows, warming inside surfaces and air inside the home. It's a great idea to plant deciduous shade trees on the southern and western sides of the house to provide summer shade, but don't plant them directly in front of southern windows. A leafless, deciduous tree can block 20 percent to 55 percent of the sun's radiation. When planting shade trees on the south side of the house, consider that winter shade patterns are 2½ times the height of a tree, and avoid planting trees that will shade southern windows. If you have established trees, consider pruning off the lower branches to eliminate some of the solar loss. At our latitude, the angle of winter sunlight is typically no more than 45 degrees. By pruning the lower branches of a tall tree, you can minimize the amount of plant material that is blocking the sun.

In addition to lowering your heating bill, dense windbreaks provide privacy, block noise, reduce carbon dioxide and air pollution, trap stormwater runoff, increase property values and provide winter shelter and food for wildlife. By planting to create shade, trees can lower your cooling bill by 50 percent or more.


Learn more

To learn more about planting for energy conservation, go to the Colorado Master Gardener website at www.cmg.colostate.edu, select “Online Yard and Garden Publications,” and read the following:

Garden Notes 631: Tree Placement: Right Plant, Right Place

Fact sheet 7.225: Landscaping for Energy Conservation

Planttalk 1722: Evergreen Trees for Colorado Landscapes