Planting Strategies for Cool Vegetation

To make the most out of your tree-planting program, it is best to be strategic about where, what, and how to plant; choosing the right setting for your tree is critical to maximizing its energy-saving and cooling benefits. These strategies can help guide your decision on the best places around a home or building to place trees or other greenery.

Air Conditioners:

According to the EPA, one of the most cost-effective ways to reduce your cooling needs is to provide shade for the building’s air conditioner and its immediate surroundings. Not only do air conditioners consume a lot of electricity, they also become less efficient as outdoor temperatures rise. Shade from trees or a vine-covered trellis on the air-conditioner can increase its efficiency by roughly 10 percent during peak periods.[1]

Windows

Shading windows and other glazed areas is a good way to reduce heat entering homes and buildings, thus conserving energy.

Walls and structures

Planting shade trees by the west- and east-facing walls (instead of north- or south-facing walls) is the most effective way to cool down building interiors  

• Mature tree limbs should reach within 5 ft (1.5 m) of west or east walls and 3 ft (0.9 m) of south walls for optimal cooling and microclimate effects. Planting trees too close to the building can result in damage to the building foundation or potential danger from falling tree limbs.
• Tall shrubs should be planted within 4 ft (1.2 m) of west, east, and south walls. The plants should reach within 1 ft (0.3 m) of the walls after four years of growth.  
• Be careful when planting trees along south-facing walls: Choose deciduous trees – which lose their leaves in the fall – so as to not block too much winter sunlight. Do not block south-facing windows.  

Pavements and parking lots

Shading pavements can reduce outdoor surface temperatures, which in turn can help reduce the local air temperature in a community. Read our section on Cool Pavements for more information. Tree shade over a parking lot can also keep parked cars cool. This is important to reduce the evaporation of gasoline, which releases volatile organic compounds into the air, a precursor to ground-level ozone. Both Davis and Sacramento require that 50 percent of parking areas be shaded within 15 years of their construction.[2]

City-wide

To maximize the benefits of city-wide cooling, trees and shrubbery should be planted in all available spaces. Consider increasing vegetation in both public and private spaces such as plazas, street medians, parking lots, by sidewalks, residential yards, parks, commercial zones, etc.  Local governments can increase urban vegetation by including a zoning requirement for vegetation or new developments in the community.

Other tips

1. Consider planting vines while trees and bushes are young and reaching maturity. Though less effective than trees and shrubs, vines grow quickly and need less space and soil.
2. Inclusion of shrubs and groundcovers can increase cooling effects, especially if replacing concrete or asphalt.
3. Planting trees in clusters helps create a broader shadow and the trees can share soil and water.
4. If you have solar panels or collectors, be sure to not shade them!
5. Consider drawing up a solar path diagram, which outlines the sun’s path through the sky in different seasons relative to the building, to help plan the positions of trees.

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