Otte-Coleman - City Magazine

CITY WORKS |
Reducing Winter Injury
to Evergreens
By Jackson Bird, City Forester of Bismarck
Winter sun, wind and cold temperatures can
desiccate (also known as winter injury)
evergreen foliage. In the spring, many
evergreens exhibit brown needles. In extreme
cases, whole evergreen branches will appear brown or dead.
This damage usually appears on the side of the prevailing
winds, or a source of reflective heat, such as a brick wall
or street. In N.D., this damage is usually on the north or
northwest side of the tree or shrub.
During the winter months, the roots of the evergreen are
not able to absorb water from the frozen ground. Needles on
evergreens continue to lose moisture throughout the winter.
When dry, cold winter winds blow over these needles, it
increases the amount of moisture that is lost. Insufficient root
systems, root injury and soil conditions contribute to this
injury.
There are several things the home owner can do to minimize
winter injury to evergreens. The best thing home owners
can do is keep the soil adequately moist during dry seasons
and into the fall, right up to the time the ground starts to
freeze. Relying on a lawn irrigation system to water your trees
and shrubs is not enough; deep watering to a depth of 18 to
24 inches is best. Ease up on the watering in September to
encourage the plant to prepare for winter. In October, deepwater
trees and shrubs until the ground freezes.
Another thing the home owner can do to help their trees and
shrubs is to add a layer of mulch in the fall. Apply a 3 to 6 foot
diameter ring of mulch around the trees and shrubs. Apply 3
to 4 inches of mulch, but keep it 3 to 4 inches from the trunk of
the plant. This mulch layer will help conserve soil moisture and
help moderate soil temperature around the tree.
Many ask about using anti-desiccants to help with
evergreens. Unfortunately, the current research indicates this is
ineffective in our N.D. climate. They need to be applied when
the temperature is above freezing. The winter winds wear off
this product within a month, so you need to reapply a month
or so later, but by then, it is too cold to apply the product.
With a bit of preparation for winter, you can insure healthy
evergreens year round.
November 2009 35