Share on Google+
Hellebores blooming in December.

What Does This Weather Mean for the Plants?

There are cherry trees and flowering almonds blooming all over Nantucket.  Daffodil foliage is sprouting and I even saw a photo of an Iris in bloom in a protected yard near town. The buds on my Magnolia are swelling, and my Pineapple Sage is still covered in scarlet blooms! I’ve been inundated with questions and concerns about how this warmer-than-average fall weather will affect all the plants around us, as the forecast for much of the northeast is for continued El Niño-influenced mild conditions at least through January.

There are plenty of things to consider when talking about plants and weather.  For example, if you have kale, spinach, chard and other hardy greens growing, you are in luck, as you will be able to continue to harvest them for some time.  Greens will keep growing as long as there’s a little sun now and then, and temperatures remain above freezing in the daytime.  Kale just continues to get sweeter as it gets kissed by frost.  Plus if the ground isn’t frozen, it’s easier to dig carrots and beets! And leave the leeks in the ground until you are ready to eat them.

When you are talking about larger, more temperamental plants, like flowering trees, shrubs, and perennials, the mild weather creates a bit more confusion. When you consider the zone designation of a particular plant, say USDA zone 7, the temperature associated with that is 0˚F. That does not mean that the plant needs to reach that temp, but rather that it can tolerate it.  It varies, but many plants need 4-9 weeks below 45˚F in order to bloom in the spring, and I do believe those temperatures will arrive later on.

But that leads to a different problem.  If the weather pattern shifts abruptly, those plants that have been chugging along in the 40’s will not have hardened off well.  Ideally, temperatures drop steadily through the fall and into winter, allowing a plant's cells to become acclimated to colder weather according to their natural time frame.  A sudden change in temperature could mean trouble for many plants.

Don’t be too concerned about your flowering trees though.  Most trees will not expend all their blossom buds if they bloom out of season, so there will be fewer flowers in spring if your tree is blooming now.  But there will still be blooms!  I’m choosing to consider it a bonus that I can enjoy the blooms twice in one year.

The best case scenario is for temperatures to drop steadily when they do shift, and as soon as it gets cold a nice blanket of snow will fall.  Snow is a great insulator and can prevent damage otherwise caused by repeated freezing and thawing.  Temperatures below freezing also help mitigate plant pest populations by killing eggs and overwintering insects. A very mild winter usually means high aphid, mite and other insect populations through the summer.  Weeds are prolific after a mild winter as well, as fewer seeds are killed by the cold.  

There’s no way to predict which plants will suffer most during wild weather fluctuations, but here are some things to think about.  Plants planted outside their zones will suffer more.  If you plant a zone 8 tree, shrub or perennial here on Nantucket in zone 7, chances are greater that it will be damaged in winter.  It is a good idea to mulch these plants to try to minimize changes to the soil temperature. Wrapping them in burlap will do nothing to protect them from the cold, but is good for preventing wind damage.  

Because spring blooming plants usually set buds the previous year, they will likely suffer more than summer and fall bloomers that don’t set bud until the weather warms.  Your summer perennial garden is less likely to have damage than the fruit trees that are found all over the island.

One of the bonuses of this mild weather is that it’s not too late to plant your spring bulbs.  Those who are seeing daffodil foliage sprouting now should remember two things.  First, those bulbs are probably not planted deeply enough. And second, if they do bloom in January, there won’t be any long-term harm to the bulbs.  They will not bloom again this spring, but will probably bloom at the right time the following year.  

Looking forward, let’s hope for gradually falling temperatures followed by a nice comforting blanket of snow, followed by an early spring and a sun-kissed summer.  Hey. A girl can dream, can’t she?