Sunday, February 19, 2017

Getting closer but not there yet

Imagine, lying in bed nice and cozy then suddenly the duvet is whipped off. That’s bad enough, but then the window is thrown wide open and an icy blast flash freezes your tender bits. If this is repeated enough times, those bits will fall off. This is exactly what happens to plants in the garden when the snow melts quickly, as it has this week.

Snow is an insulator, the deeper the better. It keeps plants in a comfortable state of dormancy. Even in winter, soil is giving off heat. Deep down, soil temperature is around 10 degrees or so, summer and winter. Where there’s a deep layer of snow acting as insulation, the surface temperature of the soil may be barely frozen. A study from the University of Delaware showed that for each centimetre of snow cover, the soil temperature will increase by roughly half a degree Celsius. 

Being suddenly exposed to icy blasts won’t bother tough plants, especially native ones, but any tender ones will suffer. And if the icy blasts don’t get them, the soggy soil will. The ground below may remain frozen, but nearer the surface it will be waterlogged. This happens in spring, but the ground soon thaws and normal drainage is resumed. When it happens in the middle of winter, that soggy ground refreezes. Repeat a few times and the expensive, borderline hardy perennial that you planted with care last spring will quietly succumb and no amount of coaxing will revive it. The same conditions can easily cause plants that aren’t well rooted to be heaved out of the ground, dead or alive.

I haven’t reached the point where I’m pushing wheelbarrows full of snow to the backyard to cover tender plants, but I have on occasion tossed a few extra shovelfuls over one or two. I usually mulch around the special ones in fall to help them resist the effect of winter thaws.

There are places in my backyard where the snow drifts deeper, and consequently, plants below are less prone to being prematurely exposed. The same occurs in sheltered areas, usually in shade and out of the wind. It’s worthwhile to note these places as they are in effect, micro-climates. A tender plant may require other specific considerations — soil type, sun or shade etc. — but it might just stand a better chance by being planted where it won’t be subjected to harsh conditions too early in the spring.

It’s also worth noting where the opposite occurs — areas in the garden where wind consistently whips snow away to expose the soil. This happens around the base of shrubs, posts, and against a fence, or building.

The snow is often scoured away along sides of buildings, depending on the prevailing wind, although the soil may be warmed by heat loss from the house, counteracting the effect of the wind. In fact, tender plants often survive well here. For instance, spring bulbs planted close to a sheltered, south facing wall will flower days or even weeks earlier than those in the middle of a garden.  Against a fence there’s no extra heat in the soil and though the fence may cause snow to drift deeply as you may see on a leeward flowerbed, the space closest to the fence is left exposed.

It may not be immediately obvious that a change in the weather is impacting the way a garden will look in summer, but it certainly does. Ahh, summer. Brrr — hang on to that the duvet. Winter isn’t over yet.

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