HORTICULTURE What Does this Warm Winter Mean for Fruits and Other Plants?
Mark LongstrothBecause most plants do not grow during the winter we say they are dormant. During dormancy, plants track chilling hours, above 35 F and below 50 F. The plant ignores temperatures below freezing or warm temperatures above 50. The chilling hours required varies for different plants from 700 to 1300 hours or more. Chilling and dormancy normally prevent plants from beginning growth during warm spells in the middle of the winter. The very warm weather we have had since before Christmas makes me think that most plants have already completed their chilling requirement and are ready to start growing. With the return of warm weather the plant begins to grow.
The temperatures I would worry about are highs in the 50s with lows above freezing, or average daily temperature above 45. Once growth begins the plant cannot increase its ability to withstand cold and will be injured by very cold weather. There is one very easy way to know if rest has been completed. You take cuttings from the plants you are interested in and bring them inside, placing them in a vase or glass of water, to force them. If the buds begin to swell and grow within a week to ten days then you know that warm weather will cause them to grow.
Right now there has been no damage to the plants. If we get warm temperatures and then the temperatures fall into the teens below 20 then we might see damage. With the mild weather we have seen I do not think that is likely. I think it is more likely that our mild weather will continue and we will see early growth in the Spring. Perhaps growth will start in early March rather than late March. To me this means that it is more likely that we will see damage from spring frosts or freezes in March as the plants try to bloom early, than we will see winter injury in January of February.
