Will the Warm December Weather Cause Plants to Grow?
I have had some calls from residents that are worried their plants will break dormancy with all of the warm weather we have had. I told them that there is little to no chance of plants breaking dormancy right now. Many plants need certain amounts of cold weather after they go dormant in order to start growing again in the spring.
Winter cold is measured in chilling units, or hours. These units are accumulated, generally, when temperatures are between 30 and 60 degrees Fahrenheit. Different plants require different amounts of chill units before they break dormancy.
Some examples of plants that need very little cold weather to break dormancy include daffodils, forsythia and Japanese plums. These plants are usually the first to become active and have been know to bloom in February.
Plants that bear fruit like peaches and blueberries require differing amounts of chilling depending on the variety. If you are thinking about buying peach trees or blueberry bushes, do a little research, and select varieties that need over 700 units of chilling. You can often find this information in nursery catalogs.
If the weather remains cold throughout the winter, then even low chilling plants like forsythia and Japanese plums will not bloom early. Under the right, warm conditions; don’t be surprised to see low chill plants blooming as early as February or March.
One final note – NC State grape specialist, Dr. Sara Spayd, is advising people with grapes not to prune at this time. Many grape varieties need very little chilling accumulation and pruning now may cause the vines to grow. Wait until late winter to begin pruning your grape vines.