How Do I Protect Landscape Plants in Winter?

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Large dips in temperature following warm spells in winter can result in trunk splitting.

Large dips in temperature following warm spells in winter can result in trunk splitting.

January 11, 2016

Winter officially arrived on December 21 but this is the first week we have had to deal with severe cold temperatures. By the time you read this it may be warm again. In fact, as I write this the bermudagrass plot at the Pitt County Arboretum still has some green in it. The cold weather has prompted many questions about how to protect plants during winter cold. As we get into our coldest time of the year, here are some tips to protect landscape plants. For most plants, winter protection does not mean to keep them warm by covering them. Covering plants with sheets does little to protect them from the cold. We do need to protect plants from damaging wind, heavy snow and ice, the alternate freezing and thawing of the soil beneath the plants and heat from the sun on cold days.

We should protect evergreen plants by preventing water loss. Since evergreens retain their leaves in winter, they continue to lose water even in winter. Roots can absorb moisture when it is available, but when the ground is frozen or we have a dry period moisture is not available. If soil moisture is not available, water is drawn out of living cells. As a result, leaves brown and die. Take caution with susceptible plants such as gardenia, Indian hawthorn, and pittosporum. These are cold tolerant to Hardiness Zone 8 or lows down to 10 degrees fahrenheit. We occasionally get cold enough for these and other sensitive plants to get damaged. Place these in a location sheltered from wind and provide water during dry periods and prior to expected hard freezes. I notice much less damage to gardenia, Indian hawthorn, and pittosporum in light shade than those in full sun.

Most of the azaleas we grow here have enough cold tolerance that covering is not needed. In the spring or fall, flowers of spring blooming or repeat blooming azaleas may be damaged. Fortunately, it is usually the uppermost flowers on a plant that get damaged. Flowers inside the canopy are protected.

Foundation plantings are often broken by snow and ice falling from roofs. You can prevent injury by wrapping cloth or burlap tightly around evergreens to hold branches together. This support may prevent breaking from the weight of snow. If branches are bent over by snow or ice, it is best to wait a few days before pruning, since some branches will recover. Prune broken limbs as soon as possible.

You can protect landscape plant roots by adding extra mulch. Don’t exceed 4 inches. Mulch will reduce water loss from the soil. Reduction in water loss means additional protection from foliage death due to excess water loss. Rose gardeners often protect newly planted roses by pulling up to 12 inches of mulch up around the stems temporarily. This should be removed by spring.

In summary there are seven ways to protect landscape plants form cold damage:

  1. Plant only varieties hardy in our area.
  2. Locate less hardy plants in the highest part of the yard. Cold air settles to the lowest areas.
  3. Protect plants from cold wind by using fencing or a tall evergreen hedge.
  4. Shade plants from direct early morning, winter sun. The south side of the house is the worst place for tender plants.
  5. Do not apply fertilizer with quickly available nitrogen to evergreens in the fall. This encourages tender growth that may be damaged.
  6. Avoid severe pruning of plants in the fall as this makes them more cold susceptible.
  7. If you must cover plants use row cover material engineered to provide protection.

If you feel you need to cover small plants to protect them from extreme cold and can’t find row cover materials, try mounding them with light mulch like leaves or pine straw. You can even use fence wire to make a ring around them that should then be filled with leaves or pine straw. Remember to remove these after the severe cold is past. Covering with sheets does little to help plants. If you feel you must cover with sheets, burlap or blankets use two layers, try to build a frame to keep these off the plants, and make sure they extend to and are sealed to the ground with mulch or soil. Plastic provides little protection and leaves and stems that touch the plastic will be damaged. If there is no other alternative use white plastic (two layers), never black or clear, and build a temporary frame to keep the plastic off of the foliage and stems. The bottom line is if you plant what is hardy in our area there is little to worry about. I hope this helps the next time temperatures dip into the single digits.

If you have questions about gardening in Pitt County, give the Extension Master Gardener Volunteers a call at 902-1705 or email pittcomgv@hotmail.com. You can also find more gardening information online at http://pitt.ces.ncsu.edu.