LEAFLET NO: 631
Revised 9/93 -- Author Reviewed
CONSERVING ENERGY WITH PLANTS
M.A. (Kim) Powell
Never before has the demand for energy been as high -- and never
before have homeowners become so increasingly aware of the energy
savings possible with landscaping. Although it is not possible
to control temperature, wind, and other natural elements, certain
landscape practices can help modify the climate in and around the
Department of Horticultural Science
North Carolina Cooperative
North Carolina State University
By placing trees, shrubs, vines and landscape structures
properly, homeowners can reduce the energy required to keep homes
comfortable during winter and summer. Along with the reduction
of energy bills, a well-planned landscape adds beauty, interest
and increased property values.
Although homeowners have intuitively used landscaping to save
energy for many years, we are only beginning to realize the
magnitude of the savings possible. According to one government
study, winter heating bills may be reduced by as much as 15
percent, while summer cooling energy needs may be cut by as much
as 50 percent.
Houses gain or lose heat in 3 basic ways:
The role of landscape vegetation in conserving energy varies with
the different microclimates across North Carolina. In the
cooler, northwest areas of North Carolina, where enormous amounts
of energy are consumed in winter heating, control of air
infiltration is paramount. Hotter southeastern areas place more
emphasis on use of shade to control heat conduction and reduce
the need for summer air-conditioning. Three basic landscape
applications which have proven to save energy are: (1) the use
of shade trees, (2) windbreaks, and (3) the use of foundation
- air infiltration - passage of air through cracks and around
doors or through open windows and doors. The average home
loses 20-30% of heat in winter by air infiltration;
- heat conduction - conduction of heat through materials of
which the house is built. Controlling the temperature
difference and air movement between inner and outer surfaces
of walls, floors and ceilings is the best opportunity for
reducing heat conduction. Heat conduction represents up to
50% or more of the total heat exchange between a home and the
- solar radiation - heat is transmitted into homes by
penetration of the sun's rays. Up to 90% will be transmitted
into the living area if rays are received perpendicular to a
single pane. Sunlight will be increasingly reflected by the
glass as the sunlight departs from the perpendicular.
Trees. Trees can reduce summer temperatures significantly.
Shading the roof of a house from the afternoon sun by large trees
can reduce temperatures inside the home by as much as 8 to 10
Deciduous trees provide summer shade, then drop their leaves in
the fall. This allows the warmth of the sun to filter through
their bare branches in winter and helps warm the home. If a home
can be situated to take advantage of shade from existing trees on
southeast and west exposures, energy expended to cool the house
can be reduced.
If there are no existing trees, the owner can select and place
trees that ultimately will provide shade. The temptation is to
plant the fastest growing species available. However, this is
usually a poor choice for several reasons. Trees that grow at
more moderate rates usually live longer, are less likely to break
in wind and ice storms, and are often more resistant to insects
A carefully selected and planted tree with a moderate growth rate
often will respond to good care by increasing its rate of growth.
Recommended shade trees for North Carolina would include: Red
Maple, Sugar Maple, Pecan, Birch, White Ash, Ginkgo, Honeylocust,
Sweetgum, Tulip Poplar, Blackgum, Sycamore, White Oak, Red Oak,
Willow Oak, Water Oak, Bald Cypress, Linden, Zelkova, River
Birch, and Hickory.
Smaller trees such as Crape Myrtles and Dogwoods can be planted
closer to the house and used for shading walls and window areas.
Since they are deciduous, they will provide shade during the
summer and allow light and sun to penetrate during the winter
season. (See HIL #621, "The Use of Small and Intermediate Size
Trees in the Landscape".)
Always remember proportions. Ask the nurseryman or county agent
How fast? and How large? a certain tree will grow.
Another way to reduce energy consumption with trees and shrubs is
to provide shade for the outside protection of a split system air
conditioner. A study by the American Refrigeration Institute
shows that shading of this type can reduce the temperature inside
the home as much as 3 degrees F. However, shrubs planted near
the compressor should not obstruct the air flow or access for
service. In addition to reducing energy consumption, screening
outdoor air conditioning equipment with plantings enhances the
esthetic value of the home.
Espaliers and Vines. In addition to shading roof areas, plants
can protect walls from heat and cold. Vines, shrubs and certain
trees can be used as espaliers (plants trained to grow flat
against walls). The foliage cover insulates the wall against
summer heat and cold winter winds. Trees, shrubs and vines can
be highly effective in reducing noise and dust pollution.
Overhead Structures. Arbors and slatted wooden overhead
structures can be effective either attached or adjacent to the
home or farther out in the landscape. If adjacent to the home,
they provide the bonus of shading walls and windows, thus
reducing heat and glare and providing cool, restful sitting and
viewing areas. Carolina Jasmine, ivy, wisteria or grape vines
are popular vines which are well adapted to most of the state.
Protection From the Wind. Although hedges have been utilized for
many years, their value has increased with the advent of higher
fuel costs. Winter winds in North Carolina usually blow from the
northwest and accelerate the rate of air exchange between a house
and the outdoor environment. Savings of up to 23 percent have
been recorded in comparing completely exposed homes and a house
landscaped to minimize air infiltration. Summer winds normally
blow from the south or southwest with generally positive effects
on human comfort. Tall trees on the south and west can reduce
temperature while allowing breeze to pass beneath and through the
Planning Windbreaks. Windbreaks obstruct and redirect the flow
of wind. As wind strikes an obstruction, it can move over,
around or through it. The extent of protection on the leeward
side is related to the height and length of the windbreak.
Impenetrable windbreaks create a strong vacuum on the protected
or leeward side, which reduces the protection. Windbreaks
composed of living plants allow some of the wind to penetrate,
which makes them more effective.
Several evergreen trees which grow into large windbreaks and also
screen objectionable views are: Hemlock, Cedar, Southern
Magnolia, White Pine, Loquat, and Deodar Cedar.
Most homeowners need to consider the size requirements of the
living hedge. 6-12 ft evergreen shrubs for good windbreaks are:
Camellia, Sasanqua, Cleyera, Elaeagnus, Holly varieties,
Ligustrum, Waxmyrtle, Oleander, Osmanthus, Photinia, Pittosporum,
and Viburnum. If space is limited for a hedge, consider some
type of construction fence or wall.
Other Types of Windbreaks. In addition to traditional
windbreaks, shrubs can also be used closer to the home for winter
protection. This is more practical for small areas and
subdivision lots where space does not allow the use of
conventional windbreaks. For this type of protection, a
combination of dense evergreen plants and groundcovers are most
appropriate. They should be planted close enough to eventually
form a solid wall and far enough away from the house (about 4 to
5 feet, minimum) to create a dead air space. This relatively
still or dead air has much less cooling power than moving air
which can decrease the loss of that through the walls.
Evergreen shrubs which should be considered as foundation
plantings would include many dwarf or slow-growing types. This
would include Dwarf Hollies, Boxwoods or Junipers.
Good landscaping practices offer one of the most practical
methods of reducing energy consumption in homes. When the
homeowner considers the added benefits of the increased real
estate value and more attractive homes and communities, the
investment becomes an even greater bargain.
North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914.
Employment and program opportunities are offered to all people regardless of
race, color, national origin, sex, age, or disability. North Carolina State
University at Raleigh, North Carolina A&T State University, U.S. Department of
Agriculture, and local governments cooperating.