Be careful what you wish for with this mild winter

Witch hazel blossoms on February 5! Not here, but down in Longwood Gardens in Kennett Square, Pennsylvania: a public botanical and pleasure garden around which I had some time to wander before giving a lecture. One little grove was particularly fragrant and comely, with a few witch hazel shrubs with yellow blossoms, some with bright orange blossoms and some with brownish-orange blossoms.

February 5 is early for witch hazel even down there, reflecting what has been the mildest winter in memory. While many people prefer mild winters, this weather worries a lot of gardeners. Are plants going to become “soft”? Is possible cold weather in the weeks ahead going to do them in?

Call me a Pollyanna, but I have a lot of faith in Mother Nature (or, put another way, natural systems) to adapt and protect against calamities. Not that everything will necessarily keep chugging along the way that we humans like it, but that forests will remain forests – perhaps with some changes in species – and that garden plants should, in general, survive.

A few odd things are going on this winter here in the Northeast and over much of the rest of the country. First are the mild temperatures. People worry that plants might begin to grow too soon. But today’s and tomorrow’s temperatures aren’t the only things that shake plants awake this time of year. Day length also comes into play; and, no matter what the winter is like, day length is the same on any given date from year to year.

Temperatures over the past weeks and months also come into play: Plants won’t begin growth until they’ve experienced a certain number of hours of cool (not cold) temperatures, signaling for them that winter is over and it’s safe to grow. Some winters, those hours begin to accumulate in autumn and then finish accumulating in late winter, when temperatures turn cool (not frigid) again. In the South – and perhaps this far north, this winter at least – those hours could have accumulated sufficiently through winter to cause an early awakening of plants.

The first sign that many trees and shrubs show of awakening is the appearance of their flowers. These early blossoms could, in fact, succumb to subsequent cold weather. That cold could nip off developing fruits, snuffing out this year’s crop. Or that cold weather could turn, say, an early tulip blossom from a handsome red cup to a wet dishrag on a stalk. In either case, the plants themselves, except for the blossoms and fruits, should not be harmed.

The second odd thing about this winter is the lack of snow cover. Snow reflects light and heat from the winter Sun. Evergreens don’t like this at a time when their roots are cold and not especially active. The result is scorched leaves. Bark also can scorch – except that this time it’s called scalding – when the winter Sun heats up dark bark by day, and then bark temperatures plummet as the Sun drops below the horizon.

On the plus side, snow is a great insulator. It helps modulate soil temperatures to minimize alternate freezing and thawing, which can heave plants up and out of the soil. Heaving is especially a problem with young or new plants, as yet hardly rooted. That insulating white blanket also lessens roots’ exposure to cold. Without snow, less cold-hardy plants (and we gardeners are always pushing the limits) might show more winter damage.

Then again, snow isn’t the only insulator. Any good gardener mulches plants to provide nutrients, to conserve water, to build up humus and to feed beneficial soil life. I’m banking on those layers of wood chips, leaves, straw and other organic materials that I spread through autumn to protect my roots – plants’ roots, that is.

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