Daniel Gill, Merrill, Thomas A. | 6/1/2007 2:26:52 AM
By Dan Gill
LSU AgCenter Horticulturist
The heat is on, and we can expect daytime highs around 90 or above and nighttime lows in the 70s from now until September. As the days get longer and the sunlight grows 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 the 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 much as those in a house that has its walls and roof exposed to the sun. Other research reports show 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, and now is a good time to evaluate where you need to plant trees to create much-needed shade.
Deciduous trees that drop their leaves during the winter generally are the best choice. These trees let the sun shine on the house during the winter, when the sun’s added warmth is welcome, and then provide shade during the summer when it is needed.
Evergreen trees would be desirable, however, where screening for privacy is needed or if you’re looking for them to serve as a windbreak 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 should be planted on the southwestern and western side of the house to be most effective. Trees in those locations will shade the house from the most intense sun during the hottest part of the day. Planting trees to the south also will help shade the house. But trees located to the north of the house are not very effective in terms of reducing the heat in the summer.
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 the trees will become later on.
Trees also need to be the desired size and planted the proper distance away from the house and concrete-surfaced areas, such as sidewalks and driveways. Although house slabs generally are 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 trees (those that may grow taller than 60 feet) and medium-sized trees (around 45 feet) should be planted at least 15 feet away from sidewalks, driveways and the house. Smaller trees (which only reach about 20 feet tall) 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 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 the summer without some sort of shade. Properly placed trees could provide that shade. Choose small-growing trees (about 15 to 20 feet tall) for planting close to patios, since those are more in scale with the surroundings and are less likely to damage surfacing materials.
When landscaping for energy conservation, deciding on the right 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 shade is needed and where to plant the trees, remember the ideal tree-planting season here runs from November through March.
So use the next few of months to study your landscape carefully and decide where shade is needed. Then determine what size trees are needed to do the job. Keep these basic points in mind:
–Generally, medium-size trees (those that grow 30 to 55 feet tall) are suitable as primary shade trees on the average urban lot. 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 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 situations, such as a patio or deck area.
In addition to size and being evergreen or deciduous, think of any other important characteristics you might want the tree to have. Other characteristics you might want to consider are wind tolerance, attractive flowers, rate of growth, interesting bark, the overall form of the tree (more upright or spreading), trees that produce berries or nuts that help feed wildlife, attractive fall color and so on.
Selecting a tree is a very 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 later this fall or winter.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.