Living

Planting trees for shade

KENNEWICK -- In the past, I have harped on tree planting, root problems and care, but I neglected to give adequate attention to shade tree selection and location.

When you consider planting a tree, the first question you should ask is what functions do you want it to serve in your landscape?

Shade? Beauty? Block a view? Frame a view of the house?

Once you know your main purpose for planting a tree, you can then determine the type of tree to select. Shade and beauty are the two main reasons that most homeowners plant a tree.

With our extremely hot and sunny summer conditions, shade is a very sensible reason for planting a tree. A well-placed shade tree can block 70 percent to 90 percent of the sun's radiation on a sunny summer day and reduce air conditioning demands by 10 percent to 30 percent.

What does "well-placed" mean? Large shade trees (40 feet tall or more) will cast a shadow equal to their height in late afternoon in the middle of summer. Large shade trees should be planted 20 feet or more away from the house. Smaller trees can be placed closer.

Place trees so they will shade south- and west-facing windows and walls. If you're unsure of where to place your trees, draw a diagram of your house and yard, indicating the direction that each side of your home faces. (My diagram is stuck on my refrigerator to remind me.)

The lots of many newer homes can't easily accommodate large shade trees such as Norway maple, sycamore, or oaks, but the benefits of shade can also be achieved with medium and small sized trees simply by placing them closer to the house and by grouping small trees together.

Plant medium sized trees (25 to 40 feet tall) 15 feet from the house and 35 feet apart and small trees (25 feet tall or less) 6 feet from the house and 20 feet apart.

Tree shape also is a factor in providing quality shade. Columnar trees (upright and narrow) don't provide as much shade for as long as those with rounded or spreading shapes. Before selecting a tree, find out what its shape will become as it matures.

Situating trees where they will shade air conditioning units and pavement around the house (patios, driveways and sidewalks) provides additional benefits in saving energy and keeping your home cooler.

Paving reflects 40 percent of the sun's energy and stores 50 percent of it, keeping the area around the home warmer than if there was grass growing in the same areas. The more pavement, the more you need to cool your home. Shading pavement can help reduce these costs. Shading air conditioners can help reduce air conditioning costs.

When you decide where to plant your trees so you can benefit the most from their shade, consult "Recommended Trees for the Tri-Cities," which can be found on the WSU Extension Benton Franklin webpage at http://county.wsu.edu/benton-franklin/gardening/general/Pages/default.aspx.

This list was developed by local experts including arborists, urban foresters, nurserymen, and horticulturists.

Only trees that have the potential of thriving in our area are listed and divided into size categories.

* Marianne Ophardt is a horticulturist for the Washington State University Benton County Extension.

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