Lately, our weather has been keeping us on our toes and sending us mixed signals: a teasing glimpse of a perfect spring day one week then a harsh wind of a polar vortex whipping at our faces the next. We hardly know which way to dress! But just like humans, plants aren’t sure what to do when they receive mixed signals. This often leads to blooming out of season, either much too soon or way too late.
Blooming late in the year, well after the typical blooming period, indicates a stressful, plant-damaging event. We’ve seen this late- season blooming after Hurricanes Florence and Michael or other events that cause damage during a warm period. These damages lead to disruptions in plant signals which throw the plants out of rhythm causing them to open up the buds they were saving next spring.
The blooms we are seeing now are the result of alternating warm and cold during a dormant period. Plants in dormancy have a ‘chilling requirement’ that must be met before they open up in the spring. This chilling requirement is an accumulation of hours of coldness that let the plant know winter is happening, and ultimately when it is ending. If winter is consistently mild then the chilling requirement will be reduced and everything will bloom happily and early. If winter is more like the one we’re having, there’s a real risk of losing springtime blossoms. Warm temperatures and plenty of rain will coax blooms from buds, but a sudden return to freezing and below-freezing temperatures will kill the open blooms.
These warm-weather disruptions also significantly lower a plant’s cold hardiness. A great example is strawberries. Strawberries that have been hardened off by the gradual cooling of autumn into winter can withstand lows in the mid-20s; strawberries that have been yanked through alternating cold and warm temperatures have lost some of that cold hardiness, which can be dangerous to any new growth encouraged by the mild temperatures.
So what can we do as gardeners? Unfortunately, not much. For flowering shrubs and plants you are fond of, you may be able to put a cover over them on nights where the temperatures plunge. For storm-damaged shrubs and trees, clean up debris as soon as you can and avoid causing further stress. For more information on out of season blooming, contact your local extension office.
Selena McKoy is the Horticulture Agent at North Carolina Cooperative Extension in Harnett County.