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Energy Efficient Landscaping Ideas
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Energy-Saving Landscaping
Seldom are utility and beauty so completely united as they
are in the trees, shrubs, and other plants that compose
the landscape.
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Parks, wooded home grounds, and tree-lined streets are
essential not only to the spiritual and aesthetic pleasure
of human beings, but also to their physical health and to
the health of all the planet.
Concerns about the environment, particularly about the
increases of carbon dioxide in the atmosphere and its potential
for global warming, have led to increased interest in trees
and their role in the environment. Without exception, studies
have confirmed the vital role that trees and shrubs - especially
those in cities and towns - play in decreasing the build-up
of carbon dioxide. Properly planted trees can significantly
reduce the amount of energy used for air conditioning and
heating. The reduction in electric use for air conditioning
is particularly significant, since electric generation in
the major source of carbon dioxide emissions in the United
States.
Landscaping for Energy Savings
Appreciation for the cooling and sheltering effect of trees
and vegetation is as old as humankind. Intuitively we know
what studies confirm - that cities sheltered by trees and
rich in vegetation are cooler in summer and milder in winter
than cities barren of vegetation. What is new, however, is
the focus on strategic planting to achieve maximum energy-saving
benefits.
How Trees Reduce Energy Use
In the summer, trees cool homes by directly shading the
structure and preventing heat gain through conduction. They
also cool the home by reducing surrounding air temperature
through the process of evaporation - evaporating water through
pores in their leaves.
Winter energy savings from trees come from their ability
to block wind infiltration. As much as one-quarter of the
heat loss in an average home is due to air leaks. Research
on winter energy savings indicates that proper plantings around
buildings can reduce rural energy use for home heating by
10 to 15 percent.
Landscaping Principles
Successful energy-saving landscaping incorporates the above
energy-saving functions into the home landscape. Other important
factors to consider, in addition to energy saving, are:
- Selection of good quality plants. Plants should be attractive
to the homeowner and appropriate not only for energy saving
but for the soil and other site characteristics. Plants
of poor quality, unsuited to the soil and available space
and sunlight, will not survive long enough to achieve
energy savings.
- Achievement of multiple benefits. The most successful
landscapes serve more than one purpose. Beauty, privacy,
boundary definition, food, and bird habitat are just some
of the other benefits you can take into account when planning
your landscape.
Summer Cooling
Shading the home from the sun is the principal strategy
in landscaping for summer energy saving. Selective shading
is necessary, however, since Ohio's climate extremes make
it unwise simply to surround the home with trees: dense plantings
- even if deciduous trees - can create enough shade in the
winter to reduce valuable solar heat gain. Prime targets for
summer shading are:
- Windows and walls facing the west and southwest;
- Air conditioning units; and
- South-facing roof surfaces.
Factors to consider when selecting plants to shade these
locations are height (both overall and where branching begins),
breadth, foliage density, and growth rate.
Trees with broad, dense crowns (the sugar maple is a good
example) are generally more effective in providing shade than
narrow trees with open crowns. Remember, however, that each
home and yard will have its own particular requirements and
there are no absolute rules to cover all situations. The size
of the area to be shaded, its height from the ground, the
direction of the sun, and available space all need to be considered.
Some trees with dense foliage that are especially effective
as shade trees are the maples, hackberry, oaks, and lindens.
The height of the tree and the height at which it begins branching
will be important in determining where it will cast its shade.
Shading two-story homes and south-facing roofs can be accomplished
with one of the large shade trees, preferably one with an
overhanging canopy. The full benefits of such a tree will
not be realized until some 15 years after planting, but they
are well worth the wait. Although there are fast-growing trees
- poplars and silver maples, for example - that will provide
almost instant shade, roots of these trees have weak wood
and tend to have invasive or water-seeking roots, characteristics
undesirable for trees located near the house. The closer a
tree is to the house, the sooner energy savings will be realized.
The tree must not be so close as to interfere with root or
branch development, however. The exact space requirements
will be determined by the particular tree and its characteristics,
such as root spread and branching habit. Shade trees planted
directly south of the home to shade the roof should be as
close to the house as practical to achieve full benefit of
the canopy and avoid interfering with winter heat gain. What
shading there is will be from the trunks and not the crown.
Large, dense shrubs (lilacs, Amur maple and highbush cranberry,
for example) are as effective as trees in reducing heat from
the sun and have the advantage of being relatively fast growing.
(Most shrubs will grow from seedling to mature height in five
to seven years.) Several shrubs can be clumped together to
shade an area such as a one-story wall or window as effectively
as a shade tree would. Vines also reduce heat gain through
walls and windows; although less effective than trees and
shrubs, they are particularly useful as a temporary measure
while trees are growing. They - also could be used on a trellis
to shade the air conditioner.
Winter Sheltering
Using plants to protect from winter winds means planting
principally evergreens. Fortuanately, Ohioans have a variety
of beautiful, densely foliage evergreen trees and shrubs from
which to select. Evergreens planted to the north and west
of the home will interfere with solar heat gain ( as they
would on the south side) and will protect from the prevailing
northwest winds. Windbreaks similar to those planted on farms
across Ohio can be adapted to the urban home grounds. The
windbreak should be on a line perpendicular to the wind direction
and can consist of one or more rows or groupings, depending
on space available. A mixture of evergreens and deciduous
trees can be used. If there is enough space, a temporary row
of fast-growing deciduous trees can be planted upwind of the
permanent row of evergreens and removed before it interferes
with the growth of the permanent planting. Some evergreens
are relatively fast growing, however; within three years,
under good growing conditions, a three-foot high spruce will
be more than six feet high and a three-foot white pine will
have passed the eight-foot mark. At these heights, both trees
can block winds. Plantings around the house foundation are
an Amercian landscaping tradition and are used primarily for
aesthetic reasons. Shrubs planted alongside the foundation
have the added benefit of creating a blanket of air space
next to the house, protecting the house from air infiltration.
Dense evergreen shrubs such as the arborvitae and yew are
ideal for this purpose.
Buying Trees and Shrubs
Before shopping at the nursery, you should have some idea
of the kind of trees and shrubs you want to buy. Go over the
list of plants in this publication; take time to read some
of the publications listed at the end of this section; study
nursery catalogs (the library will have a collection); observe
other yards in your neighborhood and seek to identify those
trees and shrubs you particularly like.
Selecting Good Quality Plants
Your best guarantee of quality is to shop at a reputable
nursery that provides a one-year warranty on the plant's survival.
Look carefully at the plant you're thinking of buying. Many
trees and larger shrubs are sold balled and burlapped, which
means the root area of the plant is in a soil ball wrapped
by burlap. Make sure this soil ball is moist and firm. If
the plant is in a container, check to see that there are no
weeds sharing the container. The plant's foliage should be
in good condition, not discolored or spotted. Some nurseries
sell trees bare-root, this is, trees which have had the soil
removed from their roots and have been held in cool storage
over the winter. The advantage of bare root plants is their
relatively low cost and the fact that the buyer can see the
quality of the roots. A disadvantage is that they must be
handled very carefully in the planting process to ensure their
survival, and they must be planted in early spring.
What size to buy
The temptation to buy large is strong for the person anxious
to reap the energy-saving benefits of trees and shrubs. Small
plants cost less, however. They also are likely to experience
less transplant shock and could catch up or even surpass the
larger plant in a few years. Some tree species grow much faster
than others, but if you are set on having shade as soon as
possible, it would be better to pay the money for a good big
tree rather than buy a fast-growing small one.
Tree Planting and Care
Spring is the best time for planting trees and shrubs,
since it allows plants to become well established before harsh
winter arrives. Most trees and shrubs can also be planted
in summer and fall, but care must be taken to provide adequate
moisture during the hot summer and dry fall. Evergreens should
be planted before October 1 to allow time for root development
before harsh, drying winter winds arrive. Bare-root trees
and package trees (trees with bare roots packed in moist materials
such as peat should be planted each in the spring; the roots
on these trees must be kept moist and protected from the sun.
Trees and shrubs in containers, and balled and burlapped trees
can be planted in spring, summer, or fall.
Properly digging and preparing the planting hole is the
first step in successful tree planting. Size and soil condition
are extremely important. Before digging the hole, make sure
there are no underground utility lines or cables in the area.
For the location of any underground utility equipment, call
the Ohio Utilities Protection Service at 1-800-362-2764. Also
check for overhead wires that could conflict with the mature
tree.
New Tree Care
Ample water is essential for the new tree or shrub. The
amount of water required depends on soil type and the tree
species. Avoiding wasteful use of water is important, especially
during dry periods. Placing the hose at the base of the tree
and releasing a slow trickle of water until the soil is thoroughly
soaked is the recommended method. Adding mulch (wood and bark
chips are good material) around the base of the tree is also
recommended; mulching keeps the soil moist, limits weed growth,
and helps prevent injury from lawn mowers and weed whips.
The mulch should not exceed four inches thick and should be
at least six inches from the trunk (not in contact with the
trunk). Fertilizing and pruning are important to tree health,
although new plants should not be fertilized during their
first year. Never prune oak trees between April 15 and
July 1. Pruning during this period could spread oak wilt,
a disease fatal to oak trees. Winter protection is especially
important for new trees and shrubs. In the fall, the trunks
of new planted, thin barked trees should be wrapped, from
the ground up to the first branch, with a commercial tree
wrap. The wrap will also help prevent rodent damage; additional
protection can be provided by placing a cylinder of one-quarter-inch-mesh
hardware cloth around the trunk. Wrap the trunk each winter
until the bark has become thick and furrowed.
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Oberlin Municipal Light and Power
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