Landscaping for Energy Conservation
Landscaping designed to reduce the heating and cooling load of a building can greatly reduce its energy needs. Vegetation can greatly reduce unwanted heat gain by keeping the sun from directly striking a building and preventing reflected light from entering. Trees, shrubs, and grass additionally provide cooling through evapotranspiration. Vegetation also affects wind velocity, and depending on plant locations, can protect a building from cold winter winds, slow air leakage, and funnel cool summer breezes into the building.
On the south and east sides of a house, the goal is to reduce unwanted heat gain in the summer, while allowing the sunlight to enter the building in the winter. A deciduous tree will provide shade in the summer and lose its leaves in the winter, but even without their leaves, trees can block as much as 60% of the sun’s rays. Solar heated buildings in colder climates may want to avoid trees on the southern side of the house entirely, and use other methods for preventing unwanted summer heat gain, such as overhangs and annual vines.
On the west side of the house, the primary goal is the block the low afternoon sun in the summer. In that case, deciduous trees with crowns lower to the ground are a good choice.
Turf and groundcovers provide cooling through evapotranspiration, and don’t convert as much sunlight in to heat like heat-absorbing materials such as asphalt and concrete. The temperature above groundcover will be up to 15 ° F cooler than above asphalt, gravel, or concrete.
When trees are too young to provide shade, or in locations where trees are undesirable, vines can shade walls and windows.
A windbreak is a barrier that blocks and redirects wind. It should be placed perpendicular to the prevailing wind direction. In many areas, wind breaks are constructed on the north side of a building to protect against cold winter winds. Evergreen conifers are the most common plant used in windbreaks, due to their dense, year-round foliage, and the fact that their foliage usually extends all the way to the ground. If snow tends to drift near a building, plant low shrubs on the windward side of a windbreak. The shrubs will trap the snow before it blows next to the building.
The height of a windbreak is the most important factor in determining how much area downwind will be protected. On the leeward side of a windbreak (the side away from the wind), wind speed can be reduced as far downwind as thirty times the height of the windbreak. For example, a windbreak where the tallest trees are 20 feet tall reduces wind speed for as much as 600 feet downwind. For maximum protection, plant a windbreak a distance from the building you want to protect equal to two to five times the mature height of the trees in the windbreak.
Landscaping for Water Conservation
Landscaping has an impact on both water use and water quality.
Landscaping to conserve water involves choosing plants that will thrive in their microclimate with minimal watering. Usually this involves limiting turf areas and instead planting species adapted to local conditions. Improving the soil and using mulch helps soil to absorb water, keeps plants cool, and minimizes evaporation.
If the actual water needs of a field or plant can be determined, then over-watering (and wasted water) can be avoided. If watering is required, it’s best to do so early in the morning when evaporation rates are low, and to specifically target watering on plants that need it.
Plants can help to manage runoff and pollution from impervious surfaces such as driveways, sidewalks, and gutters. For example, a rain garden is a planted depression that captures runoff, and allows the water to gradually permeate and be filtered by the soil. Choosing and maintaining landscape plants that require little or no fertilization or pesticide application also protects the water quality of nearby streams and ponds.