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Winter weather can chill container plants to the roots

You don’t need to watch the nightly weather forecast on your television station to know that there’s a chill in the air. Plants

feel it too, and, just like people, need to bundle up for the winter.

Plants that have poorly established roots or are experiencing stress are more susceptible to freeze damage. Lack of moisture can also make freezes more damaging. Watering landscape plants during fall and early winter will help to reduce winter injury.

Mulching is one of the best lines of defense for perennial plants against chilling temperatures. Mulching can also prevent the repeated freezing and thawing of soil that causes plants to “heave” out of the ground.

Wintry conditions can also chill container plants to the roots, resulting in poor plant health in the subsequent growing season or even death. Containerized plants are far more susceptible to winter injury because the soil freezes from all sides and plant roots are far less hardy than the top part of the plant. When plants are placed in containers they do not have the heat from the soil that would otherwise help them overcome freezing temperatures.

Plants and trees that grow naturally in the soil have geothermic heat to keep their roots cozy. For container plants, plastic actually acts as a barrier and the heat is lost in the surrounding air. As a result, roots of container plants are subjected to ambient temperatures, and freezing temperatures can kill young and mature roots.

Young roots are considerably less hardy than mature roots. Young roots are also the ones found on the outside edge of the container where they are the most vulnerable. Even if only the young roots are injured and the mature roots are adequately protected, growth next spring would be stunted and delayed. Damage to container plants can be greatly reduced by putting them in a cool garage, greenhouse or simply burying the containers in sawdust or ground bark.

Q: We have noticed that some people have wrapped their tree trunks with burlap. Should we be doing this?

A: The bark on both ornamental and fruit trees can sometimes be damaged during the winter months if we have a real cold snap. The purpose of wrapping tree trunks with a protective material like burlap is to keep the trunk from heating unevenly on bright, sunny, winter days. Bark has a tendency to split as it cools rapidly after the winter sun has warmed the south and west sides of a tree. The burlap is commonly sold as tree wrap, which is available at most retail garden stores.

Be sure to remove the protective wrap at the end of the winter season. Painting trunks with white latex paint is a technique used in commercial orchards to achieve the same results.

This column is printed as a service of the Washington State University Extension Office at Elma. Donald D. Tapio is the regional gardening and farming specialist for Grays Harbor and Pacific counties. He can be reached at (360) 482-2934 or tapiod@wsu.edu.