A tree-lined street isn't just nice for aesthetics—deciduous trees help keep summer sunlight out and allow winter sunlight in.
Look at an old family farm almost anywhere in this country, and you’ll see how crucial shade trees were before the advent of home air conditioning in the 1950s. In the midst of vast, flat fields of crops, you’ll often see a farmhouse and outbuildings, towered over by the biggest trees around. In summer, those trees shade the home and yards; in winter, they drop their leaves and let the sun’s warmth shine through.
Thoughtfully placed trees, shrubs, vines and groundcovers can play a big role in keeping your house warmer in winter and cooler in summer—before you even start to flip on the furnace or air conditioner. And which would you rather look at: a big shade tree, or an air conditioner’s compressor? Which would you rather listen to: birds singing in the shrubs, or the furnace coming on?
Cool It In Summer
If you’ve ever walked in the hot summer sun, then relaxed on the cool grass under a broad-leafed tree, you know what a difference shade makes. But is the power of plants enough to lessen our need for power plants? Consider this: Air temperature under shade trees can be as much as 25 degrees cooler than the temperature above nearby blacktop.
What could this mean for your air-conditioning costs? A landscape designed for shading can reduce a previously unshaded home’s summer air-conditioning bill by 15 to 50 percent, depending on climate and other conditions. A study of mobile homes in Pennsylvania reported air-conditioning savings of up to 75 percent for well-landscaped homes over unshaded homes.
But you don’t have to wait for big trees to grow to take advantage of vegetative cooling. You can grow vines up trellises to shade walls and patios, place large shrubs on your home’s east and west sides to block the low morning and afternoon sun, and plant leafy groundcovers to cool the earth around your home and limit the reflected sunlight that hits your house. Just shading the air conditioner itself increases its operating efficiency by up to 10 percent.
About 50 percent of a home’s summer heat gain enters through windows, so focus shading there. Just remember to use deciduous plantings if you’ll also want the sun’s heat to be able to enter through those windows in winter. (See “Pick Your Best Plants” at left for suggestions.)
Breezes are your next best trick for natural cooling. First, make sure those welcome breezes aren’t being thwarted by dense plantings and landscape walls upwind of your home. Design your landscape to move the cooling air where you want it. If the breeze isn’t aimed straight at your open windows or your favorite porch, dense plantings and yard walls can deflect the airflow to where you can feel it. As a bonus, the plants will pre-cool the air before it gets to you.
You might want to add a pond to your landscape, placing it upwind of your house and favorite outdoor areas. The breeze is cooled as it moves across the pond to you. (This strategy may not be desirable in humid climates.)
Stay Cozy in Winter
Your winter needs will be the opposite of your summer needs; you’ll want more of the sun’s heat and less wind. Plants can help here, too. Take another look at those old farmhouses; in cold climates, you’ll see dense plantings north of the house, and possibly on the east and west. These slow the cold winter winds and deflect them over and around the house.
Windbreaks can be highly effective. A study performed in South Dakota showed that winter fuel consumption can be cut by an average of 40 percent when windbreaks are planted to the north, west and east of houses. Dense evergreens make the best windbreaks. A good general rule is to find out the mature height of your chosen trees, then plant your windbreak two to five times that distance upwind of your house.
While windbreaks are generally planted away from a house, shrubs, bushes and trellised vines planted near a house also can reduce fuel consumption by creating a layer of still air near the house, acting as insulation. Plant so you will have about a foot of space between your home’s outside wall and the full-grown plant, and check with your local fire department for a list of fire-safe plants.
You also can use reflection to bring more light and heat into your home in winter. Light-colored stone, concrete or gravel landscaping, especially on the south side of the house, will reflect the low winter sun into south-facing windows. These materials’ thermal mass also stores the sun’s warmth to keep the area outside your house warmer.
Pick Your Best Plants
The best trees, vines, shrubs and groundcovers for your home depend on your region’s climate, soil, topography and your site’s particulars (for example, you might have a shady lot in a sunny region). Look to local agricultural extension agents, native plant groups, master gardeners and nursery staff for advice. These resources can point you in the right direction:
“Best Trees for Your Yard,” from Mother Earth News
Recommended native plants by state: www.wildflower.org/collections
For regionally appropriate information, input “plant database” and your state’s name into your favorite search engine.
Design Your Landscape Plan
Designing your landscape and house as one unified system creates harmony between the natural and built environments, helping to achieve a beautiful, comfortable, cost-effective and satisfying home.
Study your regional climate, your local wind direction and sun angles (and how they change throughout the year), and site particulars such as grade and soil type.
Enlist help from a local nursery or landscape designer to choose plants and other landscape elements that will let in winter sun, block summer sun, deflect cold winter winds, and admit cooling summer breezes.
Study your area’s fire-safety guidelines; avoid planting highly flammable plants next to your house.
Summer cooling is enhanced by transpiration, the process by which plants move and release moisture. Trees and other vegetation pull water up from the soil, through their trunks or stems, and out through their leaves, where it evaporates. Because evaporation requires energy, it actually pulls heat from the surrounding air. This is what makes evaporative coolers effective in dry climates; plants do the same thing without all the fan noise.
Energy-Wise Landscape Design: A New Approach for Your Home and Garden by Sue Reed
Garden and Climate by Chip Sullivan
Landscaping Design That Saves Energy by A. S. Moffat and M. Schiler
“Landscaping for Energy Savings,” Sustainable Sources
U.S. Department of Energy Energy-Saving Landscaping
www.energysavers.gov, search “landscaping”
Carol Venolia is a California architect and co-author of Natural Remodeling for the Not-So-Green House. She sometimes thinks we might be better off planting more plants and building fewer buildings.