Shade trees reduce summer cooling bills

Richard Bogren, Gill, Daniel J.

A cedar elm tree shades a house, keeping away the sun’s heat. (Photo by Dan Gill. Click on photo for downloadable image; right click to save.)

For Release On Or After 06/28/03

By Dan Gill
LSU AgCenter Horticulturist

The heat is on, and we can expect daytime highs around 90 and nighttime lows in the 70s from now until September. As the days get longer and the sunlight more intense, our home air conditioning systems work harder and harder to keep the inside of our homes comfortable.

Trees that shade the house during summer can lower air conditioning bills by blocking the sun from the windows, exterior walls and roof. Air conditioners cooling a fully shaded house have been shown to work only half as hard as those in a house that has its walls and roof exposed to the sun.

Other research reports show that shade trees will reduce heat gains by 40 percent to 80 percent, depending upon their placement and density. A shade tree is a much better energy saver than an interior blind or curtain. Now is a good time to evaluate where you need to plant trees to create needed shade

Deciduous trees that drop their leaves during winter are generally the best choice. These trees let the sun shine on the house in the winter when the sun's added warmth is welcome. Then, they grow leaves during summer and provide shade when it’s needed. Evergreen trees would be desirable, however, where you need screening for privacy or as a windbreak planted on the north side of the yard to block cold winter winds.

The location of your shade trees is very important when it comes to how well they will help reduce energy consumption. Trees are most effective when they’re planted on the southwestern and western side of the house. Trees in those locations will shade the house from the most intense sun during the hottest part of a summer day. Planting trees to the south also will help shade the house, but trees located to the north aren’t very effective.

This doesn’t mean that you should completely surround your home in a forest of trees. People frequently plant too many trees on their property, not realizing how large they will become later on.

Trees also need to be the desired size and planted the proper distance from the house and concrete-surfaced areas, such as sidewalks and driveways. Although house slabs are generally not affected by tree roots, thinner concrete surfaces, such as patios, driveways and sidewalks, can be damaged by roots from trees planted too close.

The recommended distances generally relate to the mature size of the tree. Large-size trees taller than 60 feet and medium-size trees around 45 feet should be planted at least 15 feet away from sidewalks, driveways and buildings. Smaller trees that grow to be about 20 feet should be no closer than about 5 feet.

Always watch for power or utility lines when planting trees. Locate tall-growing trees away from overhead utility lines, or choose smaller-growing trees.

The size of the tree you plant depends on the size of your house, the size of your lot and how large an area you want to shade. You should choose a tree large enough to provide the needed shade but not so large that it causes problems.

In addition to shading the home, decide on other areas where shade is necessary or desirable. Outdoor living areas, such as patios, are unusable here in summer without some sort of shade, which properly placed trees could provide. Choose small-growing trees about 15 to 20 feet tall for planting close to patios; they’re more in scale with the surroundings and are less likely to damage surfacing materials.

When landscaping for energy conservation, deciding on the proper placement, number and type of trees requires careful planning, but you have plenty of time to think about it. Although summer is the time to make decisions on where you need shade and where to plant trees, remember that the ideal tree-planting season here is November through March.

So, use the next few months to study your landscape carefully and decide where you need shade. Then determine the size trees you need to do the job.

Generally, medium-size trees, those that grow 30 to 55 feet tall, are suitable as primary shade trees in average-size urban lots. These are large enough to shade your house. Avoid large trees which have a height of 60 feet or more or a spread over 40 feet, such as sycamore, pecan and live oak, unless you have a property large enough to accommodate them. Small trees, which grow 15 to 20 feet tall, are suitable for planting closer to the house and are particularly useful for shading smaller areas, such as a patio or deck.

In addition to size and being evergreen or deciduous, think about any other characteristics you might want the tree to have. These might include wind tolerance, attractive flowers, growth rate, interesting bark, the overall form of the tree (more upright or spreading), whether they produce berries or nuts that help feed wildlife, attractive fall color and so on.

Selecting a tree is an important decision. But with some careful thought and research, you will know just the right trees for your landscape when it comes time to plant them in November.

Rick Bogren

6/3/2013 9:45:36 PM
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