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Although a few of us enjoy cold winter temperatures,
most of us can’t wait for 70-degree temperatures to return, and plant
species are no different. This winter, as we sit inside our heated homes,
let’s not forget about the plants in our landscape. How can we help
our plants make it through the winter?
Let’s begin this discussion by defining a
couple of terms. An evergreen is a plant that has green needle- or
scalelike foliage year-round — pines, spruce, yews, and junipers, for
example. A broadleaf evergreen is a plant — boxwood, holly,
rhododendron, or azalea, for instance — that has green broad leaves
year-round.
If you expect a plant to survive our winter
conditions, begin by remembering the saying “right plant, right
place.” Select varieties that are cold-hardy for zone 5, meaning that
a plant can withstand low winter temperatures between -10 and -20 degrees
Fahrenheit.
Match the plant to the site location. Most broadleaf
evergreens need a sheltered site, so select a spot that is protected from
prevailing winter winds and intense winter sun. The best sites are on the
east or north side of a building. Fences or tall hedges of trees or shrubs
also provide good protection. Most broadleaf evergreens also need
well-drained, moist soil that is rich in organic matter, so you should
avoid planting these species under the eaves of a house, where little rain
falls. Remember, the more time you spend on site selection and soil
preparation, the less time you will need to spend caring for the plants.
Another way to help your plants survive the winter is
to keep them healthy during the growing season. Diseased, injured, and
nutrient-deficient plants are more susceptible to winter injury than their
stronger, healthier counterparts. Water is necessary for plant survival,
and it is important that trees and shrubs enter winter well watered. Roots
will continue to absorb water as long as the ground isn’t frozen.
Evergreens and broadleaf evergreens must have sufficient water before the
soil freezes in the winter. A tree or shrub that enters winter without
adequate soil and tissue moisture is more susceptible to low-temperature
injury. If the winter is particularly dry, consider watering on warm days
in January, February, and March.
One way to help conserve soil moisture and maintain
consistent soil temperatures is to add a 2- to 3-inch layer of mulch over a
tree’s or shrub’s root zone. This should be done in late fall,
after the first indication of frost in the ground. This late mulch
application will keep the soil cold and help reduce frost heaving
(alternate freezing and thawing of the soil).
Winter winds play havoc on evergreens and broadleaf
evergreens. Even though these plant appear to be dormant during the winter,
they continue to transpire water through their leaves, so the roots must
continue to take up moisture from the soil. Desiccation injury occurs when
a plant loses more moisture than it can absorb through its roots. You may
also have heard the condition referred to as “winter burn” or
“winter injury.” Water loss is greatest on sunny, windy days
when the ground is frozen or dry and roots cannot uptake moisture.
The amount of injury depends on the length of time
the stress was imposed. If too much moisture is lost, leaf cells begin to
die. Symptoms of excessive water loss in a broadleaf evergreen include
browning of the leaf margins, leaf rolling, and a wilted appearance. Injury
is worst on the side facing the wind. Other types of winter injury include
death or injury to flower buds, the death of a stem, and splitting of bark.
Various anti-desiccant products, also called
anti-transpirants, are available at garden centers. These products are
designed to reduce the transpiration (water loss) of foliage. However, the
usefulness of such products is questionable; some research has shown that
these compounds degrade rapidly and are not of much value. If you do use an
anti-desiccant, read and follow the label directions. Most such products
need to be applied before temperatures reach freezing and often need to be
reapplied during the winter.
With proper planning, winter damage to your plants
can be minimized.
Jennifer Fishburn is a horticulture educator with the University of Illinois Extension Sangamon-Menard Unit. Contact her at www.extension.uiuc.edu/Sangamon.
Jennifer Fishburn is a horticulture educator with the University of Illinois Extension Sangamon-Menard Unit. Contact her at www.extension.uiuc.edu/Sangamon.
