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The value of trees in energy conservation

By Mary Jane Breitling

Randy Nelson, Clay counties educator from the University of Minnesota Extension service, was the speaker at the March meeting of the Three Rivers Garden Club in West Fargo. He gave a detailed tutorial on home landscaping and distributed a brochure on saving energy with trees. The publication is from the Minnesota Department of Commerce Energy Center and claims that “strategically placed shade trees could reduce an air conditioning bill up to 25 percent and reduce annual fuel bills by 10 to 20 percent.” The following is a brief summary of the brochure.

Solar energy is an important factor in both heating and cooling of our homes, although in this northern climate we spend more on heating than on cooling. Wind also affects the indoor temperature by leaking into homes in winter. The higher the wind velocity and the greater the temperature difference between inside and outside means the more heat loss there will be.

According to the brochure, about half of the unwanted heat comes from sun shining through the windows in summer. Because of the suns’ angle most of its energy hits east windows in the morning and west windows in the afternoon. The highest energy use is in the afternoon. Contrary to what we might think it is more important to shade east and west windows than south windows.

The ideal is to plant shade trees that provide maximum summer shade and minimum winter shade. The most important place to plant shade trees is to the west of the house, secondly to the east and not on the south side. They should be planted within twenty feet from the window and grow to at least ten feet higher than the window. Trees on the south side will cast a shadow on the house in winter, keeping out the desired solar energy. In summer, the shade from south side trees falls directly below them at midday and misses the house.

Many of us already have trees to the south of the house so they should be pruned to remove their lower branches and allow more winter sun through. Keep the lower branches on trees northwest of the home to get the most shade in late afternoon. It is also wise to shade air conditioners and paved areas like driveways and patios.

Pick trees that have a broad crown of dense foliage in summer and that lose their leaves just as the furnace kicks in in fall. The amount of sun blocked by a mature tree ranges from 60 to 90 percent in summer while its twigs and branches block 30 to 50 percent of free solar energy in winter. Kentucky Coffeetree, walnut and ash have moderately dense summer shade and sparse winter branching. Some trees, such as a Norway maple, may lose their leaves very late. It is best to pick trees from northern sources, as they are more likely to drop their leaves fairly early in fall. Usually the larger the tree the more benefit it will provide, but some such as Ginkgos have branching that is too sparse and some may be too narrow to cast a good shadow.

Trees have branches and twigs that bend in the wind and break its force. They are very cost effective in sheltering homes because an area of relative calm extends downwind about ten times the height of the trees. They need to be dense enough and tall enough and there needs to be enough of them. Dense evergreens twice as tall as the building is ideal, however they should be clustered together to reduce wind going between them. Plant trees perpendicular to the primary winter wind direction, usually along the west and north sides of the property. The windbreak should be taller and longer than the building it shelters. Firs, spruces and tall Arborvitae are recommended windbreak trees.

When you select your tree from the nursery, look for a good branching structure and a root system that is big enough to support it. A smaller, less expensive tree will usually reach the beneficial size about the same time as a large tree. A container-grown tree that is three feet tall or a bare root or containerized shade tree with a one-inch diameter trunk is good.

Dig a broad shallow planting area the depth of the root ball and five times the width of the root ball. It is best to use the same dirt that came out of the hole to fill it back in. Mulch a large area around the tree with three to four inches of mulch material. One yard of mulch will cover 100 square feet to three inches and 80 square feet to four inches according to Mr. Nelson.

To learn more about tree planting and care plan to attend the Annual spring workshop at the West Fargo Public Works building on Saturday, April 20, at 10 a.m. It is sponsored by the West Fargo Urban Forestry Committee and features speakers, Dr. Todd West from NDSU and Mr. Charles Elhard from the North Dakota Department of Agriculture.