Darrell Blackwelder: Cold damage on shrubs

Published 12:00 am Saturday, January 7, 2023

Unexpected frigid weather has become almost an annual event in our region during the winter months. Leaf and stem damage is almost certain for many landscape and bedding plants. Some trees and shrubs have immediate damage while other plant damage does not manifest itself until early summer. Windy conditions during the record cold weather burns foliage of evergreen trees and shrubs. Leaf margins and tips of camellia, rhododendron and azaleas are usually the victim of excessive cold temperatures.

New plantings of shrubs and bedding plants not acclimated is also prone to winter damage. Constant freezing and thawing lifts plant out of the soil damaging roots allowing plants them to dry out. Frozen soil prevents the uptake of water and nutrients causing damage, especially to newly planted bedding plants such as pansies.

Late summer fertilization does not allow plants adequate time to harden off or acclimate for upcoming winter weather. Tender, succulent growth is commonly damaged with freezing weather, especially following a period of unseasonably warm weather.

Azalea and camellia stems and branches often rupture or crack after a sudden freeze. This damage is generally not evident until mid-May when sections of azalea shrubs turn brown and die. Ornamental cherry trees, flowering plum and other ornamentals in the Prunus family have dark, thin bark easily damaged by cold weather. The cambium layer (food conducting vessels) is damaged as the bark adsorbs heat during a sunny day and splits and cracks as the temperature plummets in the evening. Generally, these trees bloom as normal in the spring and then die almost immediately. This phenomenon may also occur to other ornamental trees such as Japanese maples. Below are a few tips that helps protect landscape plants during uncertain winter weather.

  • Select plants that are hardy to our region. Many of our plants are marginal and burn easily with temperature extremes.
  • Apply at least 6 inches of course mulch to insulate and conserve moisture during the winter months.
  • Keep plants irrigated especially during periods of dry weather during frigid weather.
  • Do not fertilize plants in late summer or early autumn with excessive nitrogen. However, plants need to be healthy. Keep the plants well fertilized and free from insects and disease during the growing season.
  • Avoid pruning in fall and early winter. Pruning stimulates new growth which is often killed with late frosts and freezes. Many crape myrtles have been killed outright by excessive early fall pruning.
  • Keep plants irrigated during late summer and fall to prevent drought stress. Drought-like conditions predispose plants to winter injury and cankers.
  • Pack potted plants close together and mulch or mound soil around pots to insulate the roots.

Darrell Blackwelder is the retired horticulture agent and director with the North Carolina Cooperative Extension Service in Rowan County. Contact him at deblackw@ncsu.edu.