Winter Plant Damage – by Linda Petite

Winter Plant Damage – Linda Petite

How your plants will fare during our recent winter snow and extended cold period depends on many factors. These include how well your plants are sheltered, the hardiness of the cultivar, and the maturity of the plant. If a plant is already under stress or in a container, they are more vulnerable to damage.
The heavy wet snowstorm last week caused some damage here in the Gardens. We had a mature Garrya elliptica ‘James Roof’ and a Mahonia X ‘Charity’ uprooted from the weight of the snow. Several branches of rhododendrons and Magnolia grandiflora snapped off.
When snow and ice accumulate on your plants, let it melt off on its own. Removing snow can often cause branches to snap back abruptly, causing damage to the plant’s circulatory system. Vertical branching conifers are the exception to this advice. Knock the snow off so that the branches return upright (Thuja and Taxus). Dessication on evergreens from cold drying winds can cause brown leaves. Wait until it warms up before pruning out injured foliage.
Plants in containers may sustain root damage due to the freezing/thawing affect. Make sure the plants are well watered.
Not only is it storms like we just had that can cause damage. Plants in the Pacific Northwest may be injured by a complex combination of circumstances rather than a single factor. The weather itself creates a variety of challenges, such as colder than normal winter temperatures, the length of the cold snap, bright sunny days with frozen soil, drying winds, and heavy snowfall.
The types of winter injuries you may see on your plants can include the following:

  • Bud and stem damage.
  • Frozen roots (container plants freeze/thaw).
  • Sun and wind can scald the leaves. This damages evergreens because they lose water through their leaves (transpire) and the roots cannot pick up water in cold or frozen soil.
  • Bark splitting at the crown of the plant where roots and stem meet is a common injury to cold temps (especially if there is no mulch).
  • Branch breakage due to the weight of heavy snow. Remove the broken branches but wait until growth starts in the spring to determine which stems are actually dead.

The results of winter injury sometimes takes months to appear.