Winter's Legacy and Spring Forward

This winter’s cold is most evident on bamboo. Clumps of tawny, dead leaves, still attached to the canes, stare out from among the trunks and stems of dormant trees and shrubs. I hadn’t realized that bamboo was so widely planted. The depth of cold isn’t what killed the canes and leaves; it was the duration of cold. Seventy miles south of here, leaves of yellow groove bamboo, Phyllostachys aureosulcata, among the most cold hardy of the thick-caned bamboos, typically stay green and fresh all winter, but even they’ve been killed.

My bamboo, before pruning

No, the plants aren’t dead; just their canes and leaves. Warm weather will coax new shoots from the roots, shoots that will push skyward rapidly. I’ve measured as much as 6 inches of elongation per day. The record for bamboo growth, not around here, of course, is almost 3 feet in one day!  (That little tidbit comes from Bamboo, by Susanne Lucas, a beautiful, new book -- in its binding, photographs, and clear writing -- that provides an introduction to the culture, horticulture, and myriad uses of bamboo. Read it and you also will want to grow bamboo. For even more in-depth information on bamboo botany, culture, and uses, I turn to the no-frills book, The Book of Bamboo, by David Farrelly. )

Once bamboo shoots stop their skyward ascent, the walls of the canes begin to thicken. Canes that survive winter with green leaves intact don’t grow any taller in subsequent years. Cane diameters remain constant as they thicken within, in so doing becoming more useful for stakes, fencing, gates, and structures in the garden and beyond. Eventually, whether winter temperatures are frigid or mild, a cane dies.

Bamboo, after pruning almost all of it down to the ground

Dead canes, weather from age or from winter cold, eventually need to be removed to keep a grove looking spry. For my planting, I decided on the dramatic approach, cutting virtually the whole planting to the ground.  I used a lopper, attacking canes one at a time, then a machete to remove side shoots with leaves from canes worth saving -- not an easy job but one that yielded an abundance of useful canes. Now, what to do with my stockpile?

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As winter freezes have segued into capricious spring frosts, seedlings need to be readied for the great outdoors. In a greenhouse, on a windowsill, or beneath fluorescent lights, these plants lead a coddled life. Outside, life is tougher: temperatures swing 50 degrees in a 24 hour period, winds whip tender leaves, and intense sunlight beats down.

What these plants need is a couple of weeks of acclimatization -- “hardening off.” Not too quickly and not too severely, though, or leaves could burn or flowers could appear prematurely; a plant could even die from shock. The thing to do is to find some cozy spot outdoors for the transplants, a spot that is sheltered from wind and receives sun for only part of the day, or else dappled sun all day. After about a week, the plants are ready to me moved to a more exposed location, one that just takes the edge off gusty winds and broiling sun. A week at this second location and plants are ready to be planted out in their permanent homes.

Seedlings getting ready of the great outdoors

The kinds of changes that hardening off induces in coddled seedlings depends on the nature of the seedlings themselves. Seedlings of cabbage, lettuce, snapdragons, pansies, and other plants that can eventually laugh off cold even below freezing develop a tolerance for cold by building up sugars in their cells. Gradual exposure to more intense light also thickens cell walls, fibers, and cuticles on both existing and new leaves. With increasing light exposure, chloroplasts, the green, light-trapping energy factories in leaves, move around and align themselves in such a way that the leaves turn darker green. And the leaves’ stomatal pores, through which water is lost and carbon dioxide and oxygen are exchanged, become more quickly able to open and close in response to changing conditions.

Cold-tender plants such as tomatoes, marigolds, and zinnias suffer at temperatures even above freezing. With these plants, chilling injury causes changes in plant membranes that interfere with photosynthesis and damaging toxins build up in leaves. Hardening off makes these plants better able to repair and prevent such damage. But temperatures that still drop below freezing mean that it’s still too early to begin hardening off cold-tender plants. Anyway, they’re still too small. Wait a month.

During the two weeks of hardening off any plant, growth slows and the plant becomes stockier. This is good; it indicates that a transplant is ready to face the world.  

Brrrr, Good Thing It's Cold.

The sound and feel of crunchy snow underfoot are reminiscent of cold, snowy winters past. Pity poor trees and shrubs; they can’t stomp their limbs or do jumping jacks to get their sap moving and warm up. The sap has no warmth anyway. Still, except for garden and landscape plants pushed to their cold limits, plants do survive bitter cold.

Peonies, delphiniums, and other herbaceous perennials opt for the easiest survival route, letting their tops die off each winter. Anticipating frigid weather way back in late summer, they pumped nutrients in their stems and leaves down to their roots. What’s left of these plants spend a mild winter underground, especially mild beneath a blanket of snow.

Low growing plants whose stems and leaves stay alive in winter have it almost as good as those survived only by their roots. Near the ground, these plants aren’t exposed to the full brunt of winter winds or cold. And when Mother Nature decides to throw down a powdery, white insulating blanket, all the better. Just in case Mother Nature wasn’t going to cooperate with that blanket, I took it upon myself to throw a blanket of pine needles over my strawberry bed to protect them from cold.

Think about it: Water freezes at thirty-two degrees Fahrenheit -- not a particularly cold temperature for a winter night -- and plants contain an abundance of water. Water is unique among liquids in that it expands when it freezes, so you can just imagine the havoc that would be wreaked as water-filled plant cells froze and burst. Yet plants that hold their heads high and upright all winter do weather the cold.

One tack is to shed those parts most likely to freeze -- leaves. That still leaves water-filled cells of trunks and stems having to stand up and face the cold.

Water doesn’t necessarily freeze as soon as temperatures drop below thirty-two degrees Fahrenheit. To freeze, water molecules need something to group around to form ice crystals, a so-called nucleating agent. Without a nucleating agent, water "supercools," remaining liquid down to about minus forty degrees, at which point ice forms whether or not a nucleating agent is present. All sorts of things can serve as nucleating agents -- bacteria, for instance -- so plants may not be protected all the way down to minus forty degrees by having their water supercool, but just a bit of supercooling may be all a plant needs to survive winter cold.

Plants have another trick for dealing with cold, one that is effective well below that minimum supercooling temperature. That trick is to gradually move water out of their cells into the spaces between the cells, where the water can freeze without causing damage. Cell membranes are permeable to water, so as temperatures drop ice crystals that form outside plant cells grow with the water they draw out of the cells. As temperatures drop, then, the plant is now threatened more by dehydration than by freezing.

One other thing at work for the plants here is something called freezing point depression, which is why antifreeze keeps the water in your car radiator from freezing and salt melts ice. Basically, whenever you dissolve something in water, you lower the resulting solution's freezing point, more so the more that's dissolved. Plant cells are not pure water, and as the liquid in those cells losing water becomes more and more concentrated in sugars and minerals, their freezing point keeps falling. Plants toughest to cold are those that are best at reabsorbing the water outside their cells when temperatures warm.

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What’s a gardener to do in cold weather? Ski, of course. Which this year is going to greatly improve my gardening.

Skiing brought me to Vermont. Vermont, besides skiing, brought me to the Gardener’s Supply (www.gardeners.com) retail store in Burlington, which brought me to their “Push Button Multi-Watering

Wand.” I contend that paying attention to and ministering to plants’ water needs goes a long way to good gardening. I’m expecting this watering wand, with options for everything from misting water, to gurgling it to making a soft shower, and more, to keep my plants even happier than they’ve been. I also like the sturdy, metal construction and, especially for watering hanging baskets, the articulating head with extensible reach.

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This year’s longer and colder reach of Old Man Winter’s fingers could help with pest problems.  Over the past few years, associated but not necessarily the result of warmer winters, the likes Japanese beetle, marmorated stink bug, spotted wing drosophila, late blight of tomatoes and potatoes, and black rot of apples have become bigger problems.

Perhaps winter cold will knock out these problems or set them back. For those that hitchhike north from warmer, more southerly locations, cold might drive those problems further south to make travel here more difficult or, at least, take longer. We’ll see.