Homeowners are concerned about the impact the recent hard freezes will have on their garden plants. The possibility of plant material suffering from freezing temperatures in the home landscape depends upon the responses to three questions.
First: Are the trees, shrubs and other plants in your landscape cold hardy? Gwinnett County is located in USDA hardness zone 7b. This means that our winter temperatures have the potential to drop as low as 10 F to 50 F. Most outdoor plants sold at local garden centers and nurseries, with the exception of annuals, some vegetables, and tropical foliage plants, should be hardy here. On the other hand, purchasing and installing plant material that is better adapted to warmer climates are at a greater risk of suffering from hard freezes.
Second: Have your plants been properly sited and planted in the yard? Some shrubs, like azaleas and camellias, can suffer from cold injury when planted in sites with open exposures to wind and full sun. Always place these plants where they will receive adequate protection from winter sun and wind.
A third question to ask is: Have the plants in your yard been properly cared for throughout the growing season? Have they been watered, mulched, fertilized, pruned and treated for pests as needed to maintain optimum vigor and growth? Weak, unhealthy or poorly maintained plants are more susceptible to cold weather extremes.
Cold injury can occur on the fruit, stems, leaves, trunk and roots. The water inside the plant parts freezes and expands, tearing cell walls causing them to leak. After a hard freeze, examine the plant material for damage; however, it is sometimes difficult to ascertain cold damage a day or even a week after a severe freeze. The damage may go unnoticed until the plant fails to come out of dormancy in the spring. A bronze coloration of the foliage, particularly on azaleas and boxwoods, may be observed just a few days after a hard freeze. On privets, ligustrums and camellias, the foliage often turns purple. The discoloration is simply the plant’s response to a sudden chill and is perfectly normal.
Azaleas, camellias, hydrangeas and other plants often experience some bark splitting as a result of hard freezes. Injury from freeze damage appears later in the year as dead twigs and branches. The damage is most observable on the lower stems closer to the soil surface.
A simple way to determine if the plant material is actually alive or actually dead is to scratch the bark with your fingernail. If the stem tissue is green or white where you scratched, that area is still alive. It should put out new growth in the spring. If, however, the stem tissue is brown or brittle, the branch is dead. The dead wood should be removed in the early spring after freezing weather has passed.
If your shrubs and trees have been properly cared for, then they should come through the winter with little or no problems. In order to lessen or prevent cold damage, follow these simple tips:
• Maintain a two- to three-inch layer of mulch around the plants at all times. It helps to insulate the root system and protect the soil from rapid temperature fluctuations.
• Avoid pruning now. The best time to shape most evergreens and summer-blooming plants is in March. Prune spring-blooming plants, such as azaleas and forsythias after flowering.
• Provide adequate water to newly planted shrubs and trees to keep them hydrated and prevent the leaves from drying due to cold air.
Timothy Daly, MS is an Agricultural and Natural Resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010.