Do you know the location of the coldest settled place on earth? Well, in case you don’t, experts believe it is Verkhoyansk in Siberian Russia.
Now, do you know the coldest place in your garden? Unfortunately, if you don’t, no-one does. I can’t provide the specific place, because it’s your garden, your space, yours to discover.
The good news is that I can give you guidelines: The location of the coldest spot in your garden depends on your house and other buildings on your lot, barriers such as fences, walls and large rocks, topography and slopes, paved surfaces, and soil types.
To be more specific, I know the general patterns of the world’s climate and hardiness zones. On a micro level, however, you are — or can be — the expert.
As Charlie Mazza, Senior Extension Associate, Cornell University says, “In the real world, we garden in micro-climates, not hardiness zones.”
What Are Micro-Climates?
Cornell University defines a microclimate as the “climate of a small area that is different from the area around it. It may be warmer or colder, wetter or drier, or more or less prone to frosts than surrounding areas.” The definition emphasizes the geographic concept of a region, usually defined as an area similar within and different from surrounding areas.
How Small is a Microclimate?
A microclimate can be as small as a garden bed or as large as a Great Lakes’ shoreline. They exist, for example, near cooling bodies of water, or in urban areas where brick, concrete, and asphalt radiate heat. Microclimates can occur anywhere.
Lake Erie Shoreline Microclimate
A case in point is the wine-growing region on the south-facing Lake Erie shores of Essex County, an hour’s drive from Windsor, Ontario.
Like most plants, grape vines thrive when they have the correct balance between warmth and coldness, sunshine and rain.
For grapes, particularly red grapes, to ripen satisfactorily they need a minimum of 1500 hours of sunshine during the growing season beginning in April and ending in October. The long hot summers of the region are ideal for growing grapes.
Lake Erie acts to moderate the temperatures, very important in the winter, as extreme cold can kill or damage grapevines. When the temperature falls below -20 C (-2 F), bud damage becomes more likely. This large body of water can cause the lakeshore region to be as much as 5 to 15 degrees warmer than it is inland.
The extra warmth also delays bud-break until mid-April, at which point the buds are out of danger of any severe frost that may damage or kill them.
The lake’s influence is also felt in the summer. By absorbing vast amounts of heat and then releasing it whenever the surrounding air and land is cooler than the water, the vineyards are able to harvest as late as the end of October without the risk of frost.
Along with sunshine, the vines also need to absorb considerable amounts of water throughout the year. Again Lake Erie sends its blessings. The vineyards grow in good soil that sits on a foundation of gravel and shale that was once an old glacial shoreline of what is now Lake Erie– about 15,000 years ago. It is perfect for the vines and it provides the perfect drainage system for any excess rainfall.
The Good, the Bad and the Ugly
Damage from the infamous polar vortex put a focus on personal gardening mistakes I made years ago when I ignored, or perhaps didn’t fully understand, the microclimates of my little space on the planet.
Most disturbing, for sentimental reasons, was the damage done to my prized evergreens: five Skyrocketing Junipers. They were given as an anniversary gift by my now-deceased mother-in-law and planted along a fence on the north side of the property.
You see, a reality of urban gardening is that an obstruction, such as a fence, wall, or large rock, not only serves to protect plants from wind, but it can also block cold air drainage, causing puddling and create the potential for very localized frost damage, particularly for evergreens.
The harsh winds during the polar vortex winter, in an area of Canada that almost never experiences harsh winters, wiped out exposed English Ivy and damaged evergreen growth to the height of the fence. And a tree with extensive dead wood, backed by dead ivy, is pretty ugly.
A west-to-east wind tunnel between the houses accentuates the damage: As wind hits a house, it creates turbulence and higher wind speeds along the wall. These areas may not be good places to plant broad-leaved evergreens or other plants easily dried out by winds.
Micro-Climates in the Garden
The good news, according to the University of Illinois horticulture educator Candice Miller, is that a gardener can create micro-climates in a garden that even you grow plants outside their preferred regional hardiness zones. She notes in “Creating Microclimates in the Garden” that your home – as well as any other buildings around your yard – will provide many small micro-climates for different types of plants.
According to Miller, the reasons for this include the fact that homes, paved areas, and heavy clay soil absorb heat from the sun during daytime, and radiate the heat out at night. Homes can also shelter out-of-zone plants from cold north-westerly winds.
An Autumn Microclimate Challenge
So why not do some research using, if you like, tulip garden bulbs?
Journey North suggests the following microclimate field exercise:
Microclimates Mean Positives and Negatives
But, as a final thought, remember this: Microclimates carry both positives and negatives. Miller notes that, “Barriers created with fences, walls, large rocks, or structures, for instance, can create cold air puddling and damage your trees. But they can also protect plants from wind and radiate heat, creating sheltered spots.”
Just school yourself in the topic of microclimates, and become aware of associated locations: warmer and colder, wetter and drier, exposed and sheltered, more and less prone to frosts. Your plants (and trees) will thank you.