CORVALLIS, Ore. – Those sad-looking landscape plants you are seeing in your yard are a direct result of recent cold weather.
Cold can damage outdoor plants by causing burst cells and ruptured bark or by scorching or burning leaves. Plant cell fluids freeze and rupture the cell wall, or tender bark is repeatedly frozen and thawed. Tree or shrub bark may eventually split, usually occurring when extreme drops in temperature hit a plant when it is completely dormant.
Large temperature fluctuations between warm and cold cause more damage than a long period of consistent cold, explained Ross Penhallegon, horticulturist with the Oregon State University Extension Service.
For instance, 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. If the plant is actively growing, sub-freezing weather will damage the non-dormant growth.
But, if the plants are dormant and the temperature remains cold during the day, there will likely be very little damage from cold.
Here are some tasks to help prevent further cold injury to your fruit trees, berry bushes and landscape plants, before the next cold snap:
Mulch all perennials with three to six inches of organic material such as shredded leaves, compost or bark chips, coarse enough to drain well. But be aware that there’s a risk that the mulch will attract voles. These rodents can girdle woody trunks, so protect mulched trunks with hardware cloth if you have vole populations in your area.
You may also mulch outdoor potted plants to prevent their roots from freezing. Better yet, move them into a protected area near a south-facing wall or into a garage.
Drape the plant with burlap or shade the plant in some way during the day to prevent the alternate freezing and thawing that causes ruptured bark. 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.
Avoid pruning plants with cold-scorched leaf tips and margins. Plants such as rhododendrons and azaleas may 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 now.”