Released August 11, 2011
NEWARK, Del. — More than a third of the U.S. had heat indexes that exceeded 100 degrees at least one day last month, according to the National Weather Service. Delaware wasn’t spared the steam bath, with record-breaking heat on multiple days, including July 22, when it hit 102 in New Castle and 104 in Georgetown.
When it’s sweltering, a tree-shaded yard looks cooler and more inviting than an expanse of lawn without trees or shrubs. But you may be surprised at just how much cooler a shady yard -- and the house in that yard -- can be.
“A mature, well-placed deciduous shade tree can reduce air conditioning costs by 20 to 40 percent,” according to Doug Tallamy, chair of UD’s Department of Entomology and Applied Ecology.
Plus, you may not need to retreat to that air-conditioned house, since the air temperature is up to nine degrees cooler near mature shade trees. For starters, tree leaves absorb solar radiation. But the biggest benefit comes from photosynthesis, as water vapor escaping through leaves cools the passing air.
Make a plan now
If your yard already has stately, decades-old maples and oaks, consider yourself lucky. But if it doesn’t, make a game plan now for what you want to plant this autumn. (Cool temperatures, warm soil and sufficient rainfall typically make fall a good time for tree planting.)
“It can be faster and easier than you realize to transform a sun-scorched yard into a shady retreat,” says Sue Barton, ornamental horticulture specialist for UD Cooperative Extension.
Tall, fast-growing native trees include species of maples, such as red and silver, as well as river birches. But don’t exclusively plant trees that will ultimately reach 40 to 80 feet high, cautions Barton. “You should try to create a canopy of tall trees and an understory of small- to medium-sized trees in your yard,” she says. “Below that, you’ll want a shrub layer and, finally, a ground layer of perennials, grasses and sedges.”
Such a landscape is attractive to the eye and also attractive to wildlife. Usually, more vertical layers mean more diverse plant life, and thus, habitat for a wider diversity of wildlife, notes Tallamy.
Planting a large tree offers instant gratification but Barton says there are several good reasons to think small. Not surprisingly, a large tree is more expensive than a smaller one. But larger trees also take longer to establish and grow than smaller ones because of more extensive damage to the root system during transplanting.
“It’s commonly said that a transplanted tree takes as many years to recover as the size of its caliper, or diameter,” notes Barton. “So a 1-inch caliper tree may take only a year to re-establish the root sytem lost during transplating, while a 4-inch caliper tree could take four years.”
Some of Barton’s favorite native canopy trees include the sweet gum, which in autumn puts on a Technicolor show of yellow, orange, red, scarlet and purple foliage, often on the same branch. (However, some trees simply turn crimson.) Black tulepo, another Delaware native, is the first tree to turn bright red in the fall. Look for it along Route 1 between Smyrna and Dover. She also likes the Kentucky coffee tree, an East Coast native that can reach 70 feet. The Kentucky coffee is relatively fast-growing and long-lived. It can tolerate heat, cold, drought, insects and disease better than many other trees and has a distinctive winter structure.
Fringe tree and ironwood are both good native understory trees, according to Barton. In spring the fringe tree has white, fragrant flowers and glossy green leaves that appear at the same time as the blooms. Ironwood features grey, sinuous bark and dense summer foliage. However, both of these trees are slow growing; if you’re looking for a faster-growing understory species consider serviceberry. This small tree offers year-round interest, including white blooms in spring, purplish berries in summer and brilliant red-orange foliage in fall. Birds like serviceberries and so, too, do many humans. “One of my friends harvested serviceberries and made several delicious pies,” says Barton.
Learn more
Need even more ideas on what to plant? Check out Plants for a Livable Delaware, a 24-page guide to superior trees and other plants that thrive without becoming invasive, now available online as a PDF.
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University of Delaware, http://www.udel.edu/udaily/2012/aug/naturalairconditioning081111.html
