Georgia Gardener Newsletter Design Tip: July 10, 2008

Shade Trees

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DeKalb County champion white oak in Decatur

In my Design Tip article of June 26 (Give Up the Grass), I briefly touched upon the temperature differences in areas shaded by trees versus open areas of grass and asphalt. As energy costs continue to rise, you may want to consider planting shade trees to help lessen your utility bills for both the summer and winter.

Everyone can easily understand the usefulness of trees to provide shade from the hot summer sun, but did you know that in the winter trees (even those that lose their leaves) can help buffer your house from cold temperatures and winter winds? Healthy trees can also add value to your home. Other benefits include the reduction of greenhouse gases since trees uptake and store carbon as they grow and they remove carbon dioxide from the atmosphere in exchange for oxygen during photosynthesis. A lesser known fact is that forested areas can actually help to ease drought by keeping the ground from drying too fast and by releasing water vapor into the atmosphere to create clouds and rain. Personally, I'm convinced our severe drought is due in part to the fact we've clear cut so many forests in Georgia that we've created dry zones in and around our developed areas.

Choose the Right Tree

Few people would argue the merits of planting trees, but choosing the right tree, installing it correctly and maintaining it are not as easy as you might think. Almost daily I see trees installed in the wrong spot, improperly planted and poorly maintained. When these trees fail to perform as expected, the tree often gets the blame.

When planting a tree for maximum energy conservation, it's best to choose a location with a southern or western exposure. This will shield you from the sun during the hottest part of the day. Measure the site to determine how much room you have. Don't forget to take into account both above and below ground utilities, water lines, septic tanks and nearby structures. You don't want to plant a tree that will grow into a behemoth in an area 25 feet wide between two houses, near the gas and water pipes and underneath some power lines. It's a recipe for heartbreak later on.

Once you have your "spot" measured out, check what type of soil you have. If the area has compacted clay, you will want to loosen that over a fairly wide area. If it's an area that stays moist or wet, you'll need to choose trees(*) that grow in those types of conditions. If this tree is to be in a lawn area, you'll want to avoid trees with surface roots1. Finally, you will want to choose a tree that is fairly fast growing yet is sturdy, long-lived and not an invasive non-native species.

There are a number of trees that are commonly planted for shade. These include many of our native oaks and maples. There are also quite a few exotic (non-native) trees used for shade, but I prefer to use and recommend native trees. There are a few native trees that are often "dissed" as good shade trees. These include pines, tulip poplars and sweetgums.

Large Trees over 50 Feet

Tree Size (HxW) Growth Drought Tolerance Native?
Pin Oak*
Quercus palustris
70x40 Rapid Good/Excellent Y
Willow Oak*
Quercus phellos
70x40 Moderate Good/Excellent Y
Overcup Oak*
Quercus lyrata
60x40 Moderate Good/Excellent Y
White Oak
Quercus alba
100x75 Moderate Good Y
Bald Cypress*
Taxodium distichum
75x30 Rapid Good/Excellent Y
Sweetgum
Liquidambar styraciflua
80x50 Rapid Excellent Y
Tulip Poplar
Liriodendron tulipifera
80x40 Rapid Good/Excellent Y
Red Maple*1
Acer rubrum
60x40 Rapid Good/Excellent Y
Hickory
Carya spp.
70x40 Moderate Good Y
Hackberry
Celtis laevigata
75x75 Moderate Good Y
American Beech
Fagus grandifolia
75x50 Slow Good/Excellent Y
River Birch*1
Betula nigra
60x50 Rapid Good/Excellent Y
Blackgum
Nyssa sylvatica
50x30 Moderate Good/Excellent Y
American Linden
Tilia americana
75x50 Moderate Good/Excellent Y
Loblolly Pine
Pinus taeda
75x40 Rapid Good/Excellent Y

Medium Shade Trees 25-50 Feet

Some landscapes just don't have the room to handle the "big guys" and you'll need to choose a medium or even small shade tree.

Tree Size (HxW) Growth Drought Tolerance Native?
Winged Elm
Ulmus alata
35x35 Rapid Good/Excellent Y
Musclewood
Carpinus caroliniana
30x30 Slow Good/Excellent Y
Loblolly Bay
Gordonia lasianthus
40x20 Moderate Okay Y
Sweetbay Magnolia*
Magnolia virginiana
50x20 Moderate Good Y
Georgia Oak
Quercus georgiana
30x30 Moderate Good Y
Post Oak
Quercus stellata
40x40 Slow Good/Excellent Y
American Persimmon
Diospyros virginiana
40x30 Moderate Good/Excellent Y
Eastern Redbud
Cercis canadensis
30x20 Rapid Good/Excellent Y
Yellowwood
Cladrastis lutea
40x40 Moderate Good/Excellent Y


Small Shade Trees Up to 25 Feet

If you have a small landscape or small area to shade, these may be your best choices. It's in this area that I don't mind using well-behaved non-native trees.

Tree Size (HxW) Growth Drought Tolerance Native?
Japanese Maple
Acer palmatum
10-25x15 Moderate Good N
Crape Myrtle
Lagerstroemia indica
Varies Rapid Good/Excellent N
Flowering Crabapple
Malus spp.
15-25x20 Rapid Good/Excellent N
Okame Cherry1
Prunus 'Okame'
25x25 Rapid Good/Excellent N
Devilwood
Osmanthus americanus
20x15 Moderate Good/Excellent Y
Yaupon Holly*
Ilex vomitoria
20x20 Moderate Good/Excellent Y
Washington Hawthorn
Crategus virdis
20x20 Moderate Good/Excellent Y

1May have surface roots requiring a larger bed or island.
*Tolerates wet or moist soil.


Planting & Maintenance

There are a few items to remember when planting trees that will greatly aid in their ability to become established and grow properly. These important planting tips (and more) can also be found in a wonderful publication by Dr. Kim Coder at UGA entitled Plant Trees Right!.

Briefly... Make sure your trees have an adequate amount of mulch by adding new mulch over the old once or twice a year. Water deeply once a week when allowed for the first 1-2 years and after that during times of heat and drought. As your tree grows you will need to enlarge the bed or island area around it by eliminating grass or ground covers. Optimally, these areas should extend out as far as the branches. If you're going to install other plants in the same bed, try to wait until the tree is established and dig carefully to minimize root damage. Never add soil over the roots of young or established trees or you may smother them and never allow invasive vines such as ivy or wisteria anywhere near your trees or your entire landscape for that matter.

In a few short years, you should be able to reap the benefits of planting trees for the betterment of you, your landscape and the environment.



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