If you live in the Southern or Mid-Atlantic states, you are most likely well aware that this winter was very mild. January 2020 was the warmest ever recorded. With balmy temperatures, we are seeing signs of a premature arrival of spring, including early flowering in cherry trees, magnolias, daffodils and camellias. But not all blossoming is happening early. For example, common eastern hardwood trees such as laurel oak, southern red oak, white oak and hackberry seem to be undergoing leaf out consistent with years past.
Why do some plants respond quickly to a warm spring and others don’t?
A variety of mechanisms inside of plants are responsible for cueing bud break. In some plants, the accumulation of springtime warmth primarily drives their springtime activity. This is common among weeds, fast-growing species and ornamental plants originating from warmer climates. Other plants, such as hornbeam, only respond to the accumulation of warmth in the spring after they have been exposed to sufficient wintertime chill. This builtin limitation prevents these plants from undergoing leaf growth at the wrong time of the season. Still other plants, such as oaks, beeches and hackberries, won’t pay attention to the accumulation of springtime warmth until the days have lengthened sufficiently.
But for plants that only require springtime warmth to sprout, this year’s warmer temperatures are ideal for triggering early leaf flushing and blossoming. The early flowering among the Tidal Basin cherry trees, is a result of exactly that. The same is true for many of the other ornamental plants that have been spotted in full bloom weeks ahead of schedule.
While seeing plants and flowers blossom may be a pleasant reprieve from the cold winter months, the effects may cause more harm than good. An early start to springtime activity can wreak havoc on our lifestyles as well as on the natural environment. For example, many of the plants responsible for exacerbating allergies flower earlier in years with warm springs, leading to a longer season for allergy sufferers. Warm winter and spring conditions can also lead to larger insect populations; when low temperatures fail to fall below freezing for much of the winter, many insects that would normally have died, survive.
Early springs can spell trouble for growers as well. Many crop species are susceptible to freezing temperatures occurring during particular developmental stages. Winter wheat is frost-tolerant in early stages, though that tolerance diminishes as the plant matures. This year, early greening of winter wheat in Midwestern states raised concerns among growers regarding frost damage in these plants. Additionally, killing freezes coming after sensitive flowers have broken bud can decimate grape, strawberry and blueberry crops.
Accelerated springs even disrupt events like the Masters Golf Tournament in Augusta, Ga. In 2017, a shockingly early spring in the South and Eastern U.S. left golfers, spectators and the media anxious that the iconic azaleas would bloom out before the Masters.
However, plants that have a chill or day length requirement to leaf out are less likely to show accelerated springtime activity. Recent research suggests that warmer winters are having the opposite effect in some cases; warming temperatures are delaying leaf flushing among species whose sprouting depend on winter chill.
The inconsistent timing of springtime sprouting or blooming between different species can have further negative consequences. Gaps in the availability of flowers can emerge, leaving insects without a food resource.
The truth is, for many plants, scientists still aren’t clear on what triggers their springtime activity. One of the biggest limitations to deepening our understanding of the cues to springtime leaf-out and flowering is insufficient observations on when these events occur. Nature’s Notebook, a program for tracking the timing of seasonal events such as leaf-out, bloom and egg hatch in plants and animals, is one way scientists are compiling the data necessary to improve fundamental understanding of plant functioning among species.
However, one thing is clear: with a rapidly changing climate, springtime activity will continue to advance in many plants. How much each species will change and what the consequences of these changes will be is not yet clear. Now — during one of the earliest springs yet — is the ideal time to start documenting how plants are responding.
Theresa Crimmins is the director of the USA National Phenology Network and a Public Voices Fellow with the OpEd Project. She holds a Ph.D. from the School of Natural Resources and the Environment at the University of Arizona.