Thursday, February 18, 2016

The Cold Garden Micro-climates


We all know that within an area, growing conditions can vary quite a bit due to micro-climates. However, what is a desirable micro-climate in a temperate area, might not be desirable in a place with cold winters like Canada or much of the northern United States.

What grows best in a protected spot is different in cold and in temperate climates



Gardeners in mild climates vaunt the virtues of a warm spot at the base of a south-facing wall, especially if it is protected from wind. Such a spot will warm up faster in spring and provide better growing conditions than a place more exposed to the elements in the same garden.

However in a cold climate garden, such a spot is often not desirable for perennials.  In such a protected place, growth usually starts too soon in the spring, and the risk of frost damage is much higher than in less protected spots where growth will be delayed.

In our cold climate, you will want to site your hellebores in a place where they won't bloom too early

In cold gardens, the desirable spot  is one where snow tends to accumulate over the winter. In such a place growth begins later in the spring, only after most of the snow has melted. By the time that snow-covered plant does start to sprout, all dangers of frost are usually over.



Snow is welcome in cold gardens as it provides insulation from bitter cold. The most desirable thing for a cold climate gardener is a reliable snow cover that comes in December and does not leave till March. Under a foot of snow, temperatures at ground level will hover around the freezing point, even if it is -20 or colder above the snow.

What kills plants in our cold climate is a warm spell that melts the snow, followed by a sudden hard frost. In areas of the garden where snow tends not to melt easily, plants are protected from severe temperature fluctuations.

For us, wisteria is border-line hardy, you will want a western exposure to ensure flower buds develop as late as possible

Large bodies of water also make a big difference. Roche Fleurie is on a narrow stretch of land between Lake Huron and Georgian Bay. In the autumn it takes a long time for all this water to get cold, so autumns tend to be warmer than 100 miles south where there is no lake effect.

But in winter, all this water freezes and consequently the air tend to stay cooler for a longer time in spring, because we are surrounded by ice. Spring is earlier 100 miles south.

The proximity of large bodies of water tends also to produce evening fogs which help a lot with moisture

Exposure also produces different results in warm and cold gardens. In a warmer climate, for a southern exposure, you will select plants that can take a lot of heat such as zinnias. In a garden where summers are cool, too hot is not as much of a concern. There the selection of plants for a hot southern exposure will be wider because that southern exposure likely won’t produce too much heat anyhow.

Finally, favorable microclimates in cold weather gardens make a bigger difference for perennials than they do for trees and shrubs.  Let us say you are in a zone 5 (where temperatures can go down to -10, -20 F) and for a couple of nights temperatures go down to -25F.  Even grown in a favorable microclimate, your Japanese maple might not make it, but your zone 5 perennials will have a better chance of surviving ( in fact they are unlikely to suffer at all if they are covered by snow).








24 comments:

  1. Thinking about micro-climates may become more important for me in my zone 6 garden. This winter continues to have many swings in temperature and not much snow cover. I now worry that my new bulbs may die due to these fluctuations if I did not plant them deep enough. I now burlap my Labrador Tea (a circumpolar shrub)against sun burn, and last year one of my azaleas' flower buds all died from early frost. So, a very timely post Alain.

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  2. With global warming I think we will all have to rethink how we garden. In the Bruce the snow cover used to be completely reliable but not this year. I hope I have not lost too many things.

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  3. Fascinating Alain, I used to grow mainly alpine plants and, as with most others, was happier the longer they were covered in snow as in their native habitat, it was not so much the temperature as the damp which killed.

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    1. Actually cold winters are very dry. You can put laundry out to dry at -15C. The clothes will first freeze solid but after a while they will all be dry.

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  4. You always write about something interesting Alain. I must say I am worried about the lack of snow cover here this winter and the wild swings in temperature. This spring I may find that I have lost a few plants.

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    1. Let us hope we do not lose too much. It looks like we will soon know as it appears spring might be early this year.

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  5. Do you find that the cold winters kill lots of bugs or have you as many as the rest of us.

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    1. You are right Sue. It is one of the few advantages of these cold winters.

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  6. very interesting Alain - not only your accurate analysis but also the challenges you face

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  7. Excellent post! We've had a mild winter here in the Midwest. Usually I'm a USDA zone 5, but this winter was more like a zone 6 or 7. We had one week when temps hovered just above and below 0F, but most of the winter our highs were in the 10sF and 20sF. I have my Hellebores near a stone wall. The temperatures don't fluctuate as much there, and it's warmer than other areas of the garden. Plus, the snow builds up and melts slowly so they have plenty of insulation. It's still always tricky to know when to rake away the mulch and encourage them to bloom. I know they're hardy, but I always want to delay the bloom as much as possible so the blooming won't be cut short by a sudden cold snap. Gardening in any place is tricky, but you've described great points about cold-climate gardening and microclimates!

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    1. The present winter is also much milder in Ontario. In our climates, a warm winter brings in an earlier spring but is more "dangerous" for plants than a cold one.

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  8. Very interesting and thoughtful post, Alain! Thank you. I haven't tried with Wisteria so far, as I always thought our zone 5 would kill it. How you keep yours? Any protection for winter?

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    1. Hi Tistou,
      Usually wisteria survives the winter in zone 5. The problem is that the flower buds tend to freeze before they open. This why the plant should face West so the flower buds come as late as possible. Here I have one wisteria that has never bloom. The picture in this post was taken in my old garden which was much warmer than the one I have now. But even there, many years the wisteria did not bloom. You should try it.

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  9. A good discussion. For me, the south and west-facing brick walls are the best microclimates.

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  10. This is fascinating, Alain. It all makes very good sense and underlines the importance of thoroughly understanding your plot and a plants' requirements. Your comment about Wisteria is interesting too. Back in the 1990s I lived in a cottage in Essex where an old Wisteria grew in a very protected walled garden. An air frost hit on 8th May and wiped out all the flowers, which were just opening. It was so shocking that I can remember the date, even though it happened 20 years ago. The plant and its environment appeared to be well matched; and the Wisteria probably hasn't been affected like this since, but I do wonder after reading this post, if the plant might have coped better in a less protected environment, since the flowers would probably have opened later. I shall watch the Wisteria here this year with interest (it is on a much colder, more exposed site).

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    1. Here at least wisterias have a better chance to bloom if they do not bud early.
      I have a similar date I remember. In 1982 the first frost was on August 20th! Normally it is only in October.

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  11. Interesting thoughts, Alain. This winter here was without snow and with frost -25C (-15F) so as you write about micro climate I'm afraid now if some of my plants survived or didn't. I tried to grow wisteria but it died the second winter as some hybrid tea roses.

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    1. As a joke I call hybrid tea roses "annual shrubs". That is what they are under our climate!

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  12. Hello Alain, I continue to find it almost impossible to imagine gardening in a place with such extremes of temperature requiring special treatment for plants that wouldn't make it through without. Setting roses down to the ground, wisteria being only border-line hardy, treating perennials as annuals. The point about not starting growth too early is a good one. I've planted several fruit trees in a colder part of the garden so that they blossom later, hopefully after the risk of frost is over.

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  13. Well, gardening is certainly made much more difficult under our climate. However, as a compensation, our winter days tend to be cold but also dry and very bright, the snow reflecting the sunlight.

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