Despite the fact that snow covers the ground as I write this, it is, in fact, spring; and spring means, among other things, the appearance of plants, sometimes from garden beds where you’d swear there was nothing but a few dry sticks. Suddenly green shoots spring up, and before you know it, flowers are growing just where flowers grew the year before. But surely fragile flowering plants couldn’t have survived a Saskatchewan winter when even hardy Saskatchewan farmers found it necessary to fly to Arizona…or could they?
The fact is they could, and do. Plants, the dominant form of life on this planet in terms of total biomass, have adapted to every ecological nook and cranny, and when your cranny is cold and your nook is numb, you’d better be able to adapt.
Plants come in three basic flavours: annuals, biennials and perennials. Each deals with the change of the seasons in a different way.
Annuals deal with the onslaught of winter by dying. That might seem drastic (even I, a transplanted Texan, wouldn’t go that far), but it works. Their trick is to live out their whole lives in the span of half a year, sprouting, growing, flowering, reproducing and then dying, leaving behind a fresh crop of seeds from which a new generation grow the following year. The tender, water-filled cells of stems and leaves can’t survive winter because water expands as it freezes, rupturing the cell walls. Seeds, however, aren’t as fragile. Insulated by other plant material, dirt or a nice layer of snow, they live to sprout another day. Seeds of some plants can lie dormant for years until conditions are right for them to germinate.
Biennials take a slightly different approach to the problem of winter. They spread their life cycles over two years. During the first year they concentrate on developing roots and foliage. The roots, safely insulated by the soil, remain alive, though dormant, through the winter months; then, in the second year, as the soil warms, moisture returns and sunlight increased, they sprout again, this time drawing on the resources provided by their well-established roots to flower, usually in late spring, and produce seeds, usually by midsummer. Then in the fall they die, leaving their seeds to perpetuate the species when the time is right.
Perennials, however, are the winners in the “toughing-it-out” category. Like biennials, they produce no flowers in their first year, instead concentrating on roots and foliage. Their roots, too, remain dormant over the winter, and the next spring, the plant sprouts again, and this time, it flowers and produces seeds. But unlike the biennial, a perennial doesn’t then die; instead, it repeats that cycle every year, going dormant in the winter, then reawakening in the spring and flowering again. Perennials will continue to survive and grow as long as environmental conditions remain favorable.
(Of course, all of this assumes that the perennial in question is being grown in the climate it is suited for. There are many plants that are perennials in their native, more southerly habitats, which can be grown in the north by gardeners, but must be treated as annuals because, although they can survive the mild change of seasons back home, they can’t survive the harsher change in weather up here.)
Perennials can be further divided into “herbaceous” perennials–the kind with the soft stems that die down in the winter–and “woody” perennials, of which trees are the best example; their stems remain in place and new growth in the spring simply adds to them, which is why trees grow so tall.
Perennials have another trick up their sleeve, in that they don’t rely just on seeds for propagating themselves. Many of them also perpetuate themselves by spreading their roots, or, more properly, their rhizomes–underground stems which grow roots on their lower sides and shoots from their upper sides. Cut and replanted, they yield new plants; left alone, they’ll soon spread into all the available space.
Bulb plants, such as tulips and onions, use a slightly different approach. A bulb is actually a mass of overlapping leaves on a short stem. They enclose and protect the bud of a new plant, and also provide food for it as it begins to grow, giving it a head start on life. Not only can bulbs survive cold weather, some of them require it. Many bulbs must be chilled to freezing or below for several days before they’ll start to grow.
Plants’ growth in the spring is activated by environmental factors, although the precise mechanisms vary from plant to plant and aren’t perfectly understood in any of them. Certain wavelengths of light, for example, apparently affect the activity of plant pigments, which in turn interact with hormones, which in turn regulate flowering, leaf expansion, stem elongation, seed germination and other plant functions. These kinds of mechanisms (temperature, nutrition and other factors also play a role) are how plants “know” that it’s spring and it’s time to start growing again. That they’re not infallible is demonstrated when plants are “nipped in the bud” by an unexpected late frost.
The sensitivity of plants to environmental factors is precisely why gardening is such a challenge. After all, it’s basically an attempt to get a bunch of different plants that would never grow together in the wild to all co-exist happily in a relatively small space. You have to know when to plant, when and how much to water, how much fertilizer to apply, when to prune, when to weed, when to dig and when to spray. The challenge of gardening must be part of its appeal, and I admire those who are up to meeting that challenge, and I love viewing a beautiful garden, but it’s not for me. My own garden grows just one type of plant, and I don’t even put it there: my landlord does.
Anyone for a potato?