By Carol Savonen, OSU Extension News
Cold can damage outdoor woody plants. Plant cell fluids freeze and rupture cell walls, resulting in ruptured bark or scorched leaves, explained Ross Penhallegon, horticulturist with the Oregon State University Extension Service.
The amount of temperature fluctuation from daily high to low usually affects how well plants will fare in subfreezing weather.
"A night of extreme cold followed by warming during the day on the south and west sides of the plant can cause bark to split and foliage to become scorched, or frost-burned," said Penhallegon. If the plant is actively growing, sub-freezing weather will damage the non-dormant growth.
On the other hand, if the plants are dormant and the temperature remains cold, there is rarely much damage from cold.
The key is to protect the plants as best as possible from the cold. Penhallegon recommends the following tasks to help minimize cold injury to your fruit trees, berry bushes and landscape plants:
* Mulch all perennials with three to six inches of organic material such as shredded leaves,
compost or bark chips, coarse enough to drain well. Also, mulch outdoor potted plants to
prevent their roots from freezing.
* Prevent ruptured bark by draping the plant with burlap or shading the plant in some way
during the day to prevent the alternate freezing and thawing. Or paint the tree or shrub
bark with white exterior latex paint to help avoid splitting. Mix the paint one to one with
water. Check the plants in a few weeks to see if there is bark damage.
* Once plants get cold, keep them cold rather than allow them to thaw during the day and
freeze at night. It is the freeze-thaw action that does the damage.
Scorched leaf tips and margins (desiccation) are a common problem after a cold spell, particularly in broad-leaf evergreens including rhododendrons and azaleas. They take on a droopy look. Dry cold winds are often the cause.
"The injured leaves will eventually drop," said Penhallegon. "In most cases, the plant will recover in the spring, so don't prune the plants until then."
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