January 18, 2011

Top 10 Winter Threats to the Garden

1. Severe
Cold

Climate change doesn’t just mean warming;
it means weather extremes. An unusually mild winter might easily be followed by
a winter with record lows. Gardening zones were created to provide a guideline
for whether a particular plant will survive in the intended area. But when the
weather doesn’t comply with these maximum/minimum temperatures (or when
gardeners cheat the zones), plants suffer and may even die. Rapid drops in
temperature may cause frost cracks in trees, which can lead to decay.

2. Sun
Scald

On cold winter days, the sun can heat bark and
fool the tree into starting growth. When the sun is blocked, bark temperature
drops rapidly, killing the active tissue. The resulting sun scald creates
elongated, sunken, dried, or cracked areas of dead bark, usually on the south
or southwest side of a tree. Young trees, newly planted trees, and thin-barked
trees are most susceptible.

To prevent sun scald, wrap the trunk with a
commercial tree wrap, plastic tree guards, or any other light-colored material
to reflect the sun and keep the bark at a more constant temperature. Put the
wrap on in the fall and remove it in the spring after the last frost.

3. Desiccation

Frozen soil makes it more difficult for
trees and shrubs to take in water. Add winter sun and wind and the result is that
foliage is giving off more moisture than it can take in. This causes wilting, browning
or bleaching of evergreen foliage. Reviews are mixed on anti-desiccant sprays,
but you can make sure plants are watered well in early winter and wrap
sensitive plants that are located in exposed areas.

4. Road
Salt

You wouldn’t water your garden with
seawater, but that’s essentially what happens when plants are in areas where
road salt is applied frequently. The worst damage occurs to sensitive species
planted near heavily salted roads with high traffic, especially when they lie
downhill, downwind, or have poor drainage. Plant salt-tolerant species in these
areas. You can also flush the soil with plain water at the end of winter.

5. Wind

Winter wind increases moisture loss, but
can also lead to breakage, especially if branches are already weighted down
with snow or ice. Prune trees and
shrubs to remove weak branches. Avoid species like the Bradford pear (now
considered invasive) that are prone to breakage.

6. Snow/Ice

Even strong healthy limbs of deciduous
trees and shrubs can break if the ice or snow is heavy enough. If the ground is
saturated prior to a heavy snow or ice storm, and enough weight is placed on
the upper portion of a tree, it can lift the root system right out of the
ground. If possible, just after a snow, take a soft broom and lift gently
upward from below, shaking the snow off branches (do not stand directly
underneath!). This keeps the snow load from staying long enough to cause
permanent misshapen plants. Pushing down on the branches isn’t a good practice
because it may exaggerate any potential damage.

7. Freeze/Thaw

Repeated freezing and thawing of soil
causes soil to expand and contract, which can damage roots and heave shrubs and
new plantings out of the ground. A 4- to 6-inch layer of mulch will prevent
heaving by maintaining more constant soil temperatures.

8. Rodents

In the winter, small rodents will often
gnaw at the base of trees, particularly if mulch (or snow) is piled up against
the trunk, providing a sheltered area in which to munch. Zigzag or squiggly
runways through the lawn are a telltale sign of vole activity. Trees can be
protected from rodent damage by placing a cylinder of ¼-inch mesh hardware
cloth around the trunk. The cylinder should extend 2 to 3 inches below the
ground line for mice and 18 to 24 inches above the anticipated snow line for
rabbits. Reducing cover by mowing can reduce vole populations.

9. Deer

Deer cause damage both by eating and by
antler rubbing. In winter when food availability declines, deer may wander
farther and eat plants they left alone when more choices were available. In
areas with low to moderate deer activity, repellents can be helpful, if applied
consistently around the perimeter to discourage entry. Once deer get into the
habit of traveling through a property it is much more difficult to discourage
them.

10. Late
Freeze

Deciduous trees and shrubs can incur shoot
dieback and bud death during the winter. Flower buds are particularly sensitive and early blooming
plants such as forsythia and some magnolias may have their blossoms ruined by a
late freeze. Little can be done to prevent this, but plants that are marginally
hardy should be placed in sheltered locations (microclimates). Also, avoid late summer pruning,
fertilizing, and overwatering, as this stimulates tender new growth late in the
season.

* Nancy Sakaduski is the Chester County
Master Gardener Coordinator. Master Gardeners are trained volunteers who
educate the public on gardening and horticultural issues. In Chester
County, they operate through the Penn State Cooperative Extension office in
West Chester. Nancy lives in Pennsbury Township. She can be reached
at nds13@psu.edu.