The Kentucky coffee tree planted about 18 feet from the southwest corner of Kris Bachtell’s Naperville home blocks enough sun with its leafy canopy that the air conditioning doesn’t have to work as hard, saving on the household’s electricity bill. In the winter, the tree loses its leaves, so the sun can pass through and help warm the house.
“It’s passive solar heating,” says Bachtell, who is vice president for collections at The Morton Arboretum in Lisle. He knew just where to place the tree when he planted it as a sapling some 30 years ago. Although any large tree near a house will provide some cooling shade, trees planted on the south to southwest side make the most difference in terms of summer comfort.
According to the U.S. Department of Energy, carefully positioned trees can save up to 25 percent of a household’s energy consumption for heating and cooling; just three to four shade trees strategically located around a home can cut summer cooling costs by 30 to 50 percent. Trees that block wind in winter also can cut heating bills.
Exactly how much energy a tree will save depends on its location, size and species. Some trees, including many kinds of oaks, have a dense canopy of broad leaves that casts heavy shade. Others, such as honeylocust, have small leaves and more widely spaced branches, casting a filtered shade that can be lovely over the patio but won’t cut the cooling bill as much.
“You wouldn’t want to plant evergreens on the south side of a house,” says Melissa Custic, coordinator for the Chicago Region Trees Initiative. Tall ones will cast shade in summer, but also block the warming sun in winter. To block winter wind and save on heating bills, she says, plant evergreens or other trees on the north or west side.
It’s important to choose a tree that is suited to the conditions of your yard, such as the type of soil and the available light, Custic says. A tree that is near enough to the house to provide shade needs to be strong, so avoid fast-growing species. “Usually, fast-growing trees have weaker wood,” she says. You can find many good options in the Arboretum’s online Northern Illinois Tree Selector.
To make sure they stay sound, trees near the house should be professionally pruned when they’re young to make sure they develop a strong, well-balanced structure as they grow. Mature trees should be regularly checked by a professional arborist who can remove any weak or damaged limbs, Bachtell says.
Planting a young tree now will pay off down the line. But preserving a large tree, tall enough to shade the house, will keep you cooler right now. Mature, substantial trees also reduce the temperature of the air around them as water evaporates from their many leaves. They filter more air pollution and do more to help manage water from rainstorms than young trees. Their cool shade is one reason studies have shown that mature trees on the property add to a home’s value — as long as they are well cared for.
And then, of course, there’s the beauty. Bachtell’s Kentucky coffee tree sapling has grown into a handsome companion that not only cools the house but cloaks it in green.
“The most wonderful thing,” he says, “is that I can look out my upstairs window every day and that tree is right there.”