Garden Microclimates: Prepare for Hot and Cold Spots in Your Garden

Does Russia own the coldest area on Earth?

Does Russia own the coldest settled place on Earth? Image by Inhakito.

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.

The Essex County vineyards near Harrow Ontario take advantage of the microclimate of Lake Erie's north shore. Image by James Gibson

The Essex County vineyards near Harrow, Ontario, take advantage of the microclimate of Lake Erie’s north shore. Copyright image by James Gibson, all rights reserved.

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.

Damage to trees from cold air puddling. Image by James Gibson

Damage to trees from cold air puddling. Copyright image by James Gibson, all rights reserved.

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.

Prevailing north-west winds of winter create winter kill on north=-facing evergreen before rushing down wind tunnel between the houses. The snow covered English Ivy was protected. Copyright image by James Gibson, all rights reserved.

Prevailing north-west winds of winter create winter kill on north=-facing evergreen before rushing down wind tunnel between the houses. The snow covered English Ivy was protected. Copyright image by James Gibson, all rights reserved.

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:

microclimate experiment

Want to try a microclimate experiment? Screenshot by Decoded Plants, all rights reserved

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.

Happy gardening!

Zone Thirteen: USDA Plant Hardiness World View

The major world concentrations of USDA plant hardiness zone 13 . Image by James Gibson.

The major world concentrations of USDA plant hardiness zone 13. Image by James Gibson.

If you live around cities such as San Juan, Puerto Rico (18°N); Cartagena, Columbia (10°N); Belém, Brazil (1°S); Kingston, Jamaica (18°N); Jakarta, Indonesia (6°S); Kuala Lumpur, Malaysia (3°N); Lagos, Nigeria (6°N); Mumbai (Bombay), India (19°N); or Mogadishu, Somalia (2°N), your plant hardiness zone is 13. This means average annual minimum temperatures are between 70°F and 60°F (21.1° to 15.6° C).

USDA plant hardiness zone 13 straddles the equator in the interior of continents (e.g. Zaire in Africa, Brazil in South America), stretching farther north where oceans and warm enclosed seas (e.g. Caribbean and Red Seas) increase their influence.

It is best known as the biologically diverse zone of the tropical rainforest; and where you find edible plants such as the banana and pineapple, spice trees such as peppercorn and cinnamon, and colorful flowers such as orchids and titan arums.

What Are Hardiness Zones?

We define hardiness zones as geographic regions, most commonly based on USDA criteria that support specific plants, flowers, and trees. They usually define a minimum range of temperature that a plant or tree can survive safely in that zone and range from the harshest zone one to tropical zone 13.

If possible it is advisable to consult other planting-related maps such as first and last frost dates, and heat zones.

Zone 13 Regions in the United States

The patterns of plant hardiness zone thirteen in the Caribbean and Central America. Image courtesy of Davis Landscape Architects. Modified by James Gibson.

The patterns of plant hardiness zone thirteen in the Caribbean and Central America. Image courtesy of Davis Landscape Architects, used with permission. Modified by James Gibson.

In the United States, the temperature range restricts Zone 13 to Puerto Rico (e.g. San Juan) and isolated parts of Hawaii. Nevertheless, it is important for residents from other zones to know about cold-sensitive tropical ornamental plants; in particular, when to bring them indoors.

The export of ornamental plants is a growing industry in Puerto Rico along with the associated threat of pests.

With modern Geographic Information Systems (GIS) which allows for higher resolution, smaller areas of zone delineations are possible. Thus, we can identify isolated parts of the zone along parts of the big island of Hawaii’s central-western coastline.

Significant Zone 13 Regions in South East Asia

The patterns of plant hardiness zone thirteen in S.E. Asia. Image courtesy of Davis Landscape Architects. Modified by James Gibson

The patterns of plant hardiness zone thirteen in S.E. Asia. Image courtesy of Davis Landscape Architects, used with permission. Modified by James Gibson 

This extremely bio-diverse rainforest area is home to shrubs such as the jambu or watery rose apple (genus: Syzygium, and species: aqueum), a small, crisp and mildly sweet, watery fruit.

The zone stretches from southern India and Sri Lanka through to Indonesia and Borneo.

Surrounded by oceans and characterized by seasonal monsoons, the resultant climate is hot and humid. By way of example, Singapore receives 2282 mm of precipitation annually.

Zone 13 Regions in Africa and South America

The patterns of plant hardiness zone thirteen in South America. Image courtesy of Davis Landscape Architects. Modified by James Gibson

The patterns of plant hardiness zone thirteen in South America. Image courtesy of Davis Landscape Architects, used with permission. Modified by James Gibson

Rainforests cover large sections of northern South America and central Africa. It’s worth noting, however, that while we think of rainforests as being rainy, in reality, compared to other rainforests throughout the world, Africa’s are drier by several hundred millimeters per year.

In Africa, the countries that have rainforests are Cameroon, Congo, Democratic Republic of Congo, Gabon, Ghana, Ivory Coast, Liberia, and Nigeria.

In the rainforest areas of Central America (e.g. Costa Rica), South America (e.g. Amazon) and along the Andes Mountains (e.g. Peru), we find the largest family of plants in the world, the orchids.

Plant Advice for Gardeners

When purchasing tropical plants such as azalea, bamboo, hibiscus, orchids, and poinsettias, be aware of related diseases. These can include many types of bacteria and fungi. Also be aware of associated beetles and weevils, in addition to moths and caterpillars found not only on the plant, but also in the soil.

In addition, always ask for a Phytosanitary Certificate undertaken by a National Plant Protection Organization (NPPO), a declaration attesting to freedom from regulated plant pests.

North American Gardeners and Zone 13 Plants

Even though Zone 13 exists in only a sliver of North America, gardeners throughout the continent benefit from knowing the needs of their Zone 13 tropical plants.

Zone One: USDA Plant Hardiness World View of the Harshest Climate

The Victory Garden by PBS list the Lapland Rhododendron as ideally suited to Zone One plant hardiness. Image by Daderot.

The Victory Garden by PBS lists the Lapland Rhododendron as ideally suited to tundra conditions of  plant hardiness Zone One. Image by Daderot.

If you live around communities such as Alaska’s Bettles or Fort Yukon; Yukon Territory’s Dawson; Northwest Territories’ Fort McPherson; or Yakutsk or Verkhoyansk in northeastern Siberia, then your USDA plant hardiness zone is One, the harshest.

This means thirty-year average minimum winter temperatures are an extreme -50 F (-45.6 C) or lower. The territory is treeless tundra where conditions for growth are harsh but suitable for plants such as the Lapland Rhododendron.

According to PBS’s The Victory Garden, USDA plant hardiness Zone One is ideally suited to plants native to the most northern areas of the northern hemisphere.

Where is Hardiness Zone One?

Plant hardiness Zone One in North America. Image courtesy of USDA and The Garden Helper, modified by James Gibson.

Plant hardiness Zone One in North America. Image courtesy of USDA and The Garden Helper, modified by James Gibson.

The zone generally straddles the Arctic Circle above 60°N with its coldest regions in the most continental parts of the world. In January of 1885, for instance, observers recorded a record low of -67.1°C in Verkoyansk, Russia. Snag, Yukon Territory, holds Canada’s officially lowest recorded temperature of -62.8°C.

Zone One’s association with very cold and stormy interior continental-type climates restricts it to the northern hemisphere. Continental climates do not occur in the southern hemisphere due to the absence of a land mass large enough and far enough away from the oceans and its currents to generate this effect.

As a compensation, however, as pointed out by the Missouri Botanical Garden (MBG), “continental climates exhibit a rapid and sustained rise in temperature in spring, promoting growth of plants and greater seasonality.

What are Hardiness Zones?

Hardiness zones consist of defined geographic regions, most commonly based on USDA criteria that support specific plants, flowers, and trees. They typically define a minimum range of temperature that a plant or tree can survive safely.

If possible it is advisable to consult other planting-related maps such as first and last frost dates, and heat zones.

Canada’s Zone One Regions

In Canada, USDA Zone One includes the tundra islands of the extreme north, the interior of the Yukon Territory, and northern Alberta. Canada’s self-explanatory designation for this area’s affinity to plant growth, however, is a designation of Zone Zero, meriting either ‘a’ or ‘b’, with ‘a’ being ‘more harsh than harsh.’

Zone One Regions in the United States

We find USDA plant hardiness Zone One in patches in the northern and central interior of Alaska including the hinterlands of Fairbanks.

USDA plant hardiness zones of Alaska. Image courtesy of USDA.

USDA plant hardiness zones of Alaska. Image courtesy of USDA.

According to PBS’s The Victory Garden the following plants grow well within hardiness Zone One:

  • Crowberry (Empetrum nigrum) is native to most northern areas of the northern hemisphere.
  • Dwarf birch (Betula glandulosa) is native to North America.
  • Lapland rhododendron (Rhododendron lapponicum) is native to arctic tundra of northern Canada, Greenland and Alaska and northern Eurasia.
  • Netleaf willow (Salix reticulata) is native to the colder parts of Northern Europe, North America, and Northern Asia.
  • Pennsylvania cinquefoil (Potentilla pensylvanica) is native to much of northern and western North America.
  • Quaking aspen (Populus fremuloides) is native to North America.
The area of plant hardiness Zone One in Russia. Image courtesy of Davis Landscape Architects. Modified by James Gibson

The area of plant hardiness Zone One in Russia. Image courtesy of Davis Landscape Architects. Modified by James Gibson.

Significant Zone One Region in Siberian Russia

In mountainous northeastern Russia, east of the Central Siberian Plateau is a large area of Zone One plant hardiness represented by Verkoyansk and Yakutsk. As pointed out by the MBG, the Russians, as in the Canadian context, categorize parts of this area as Zone Zero.

Native Plants Thrive in Low Temperatures

The low temperatures experienced in Zone One demand gardeners carefully consider what plants work best in their zone, with a preference for native plants that can not only survive, but thrive.

Zone Six: USDA Plant Hardiness World View

The major world concentrations of USDA plant hardiness zone 6 . Image by James Gibson.

The major world concentrations of USDA plant hardiness zone 6. Image by James Gibson, all rights reserved.

If you live around cities such as Juneau, Alaska; Toronto, Ontario; Halifax, Nova Scotia; Kamloops, British Columbia; Spokane, Washington; Kansas City, Missouri; Columbus, Ohio; Denver, Colorado; Boston, Massachusetts; Detroit, Michigan; Warsaw, Poland; or Lanzhou, China; your plant hardiness zone is 6.

This means your average minimum winter temperatures are between 0°F and -10°F (-23.3 to -17.8° C). Just remember, however, the wide differences in the heat zones within this area: Kansas City receives on average 61-90 days over 86°F (AHS zone 7) while Detroit checks in at 15-30 days on average (AHS zone 4).

According to PBS’s The Victory Garden, USDA plant hardiness zone 6 is ideally suited to plants of East Asian origin. The zone straddles the 38°N zone unless significantly impacted by water or elevation influences (e.g. Juneau, Alaska- 58° N).

There is a north-to-south belt of the zone 6 in the high Andes of western Argentina and southern Bolivia in the southern hemisphere. The zone, however, is primarily restricted to the northern hemisphere because of its association with very cold and stormy interior continental type climates. We don’t find continental climates in the Southern Hemisphere due to the absence of a land mass large enough and far enough away from the oceans and its currents to generate this effect.

What are Hardiness Zones?

We define hardiness zones as geographic regions, most commonly based on USDA criteria that support specific plants, flowers, and trees. They usually define a minimum range of temperature that a plant or tree can survive safely in that zone.

If possible, it is a good idea to consult other planting-related maps such as first and last frost dates, and heat zones.

Canada’s Zone 6 Regions

Plant Hardiness Zone 6 in Southern Ontario. Image courtesy of the AAFC, modified by James Gibson

Plant hardiness zone 6 in Southern Ontario. Image courtesy of the AAFC, modified by James Gibson.

In Canada, USDA zone 6 dominates the Columbia River and Okanagan Valleys of the Cordilleran Plateau of British Columbia, and the Great Lakes Lowlands south of Kitchener.

In addition it spots the southern and Atlantic coastal areas of Nova Scotia including Cape Breton Island plus the northeast coast of Prince Edward Island.

Agriculture and Agri-Food Canada lists Japanese maple (Acer palmatum), slender deutzia (Deutzia gracilis) and showy forsythia (Forsythia x intermedia ‘Spectabilis’) as shrubs indicative of this zone.

Zone 6 Regions in the United States

Plant Hardiness Zone 6 in Missouri and Massachusetts. Image courtesy of the USDA, modified by James Gibson.

Plant hardiness zone 6 in Missouri and Massachusetts. Image courtesy of the USDA, modified by James Gibson.

USDA Plant Hardiness zone 6 takes a wide sweep from patches within the western intermontane plateaus of Washington State (e.g. Spokane); they also stretch down to the higher hinterlands of Salt Lake City, Utah.

It continues northeast across the continent in a thinner belt through Kansas City, and on to Boston, Massachusetts.

With the influence of water, a leg of the zone stretches north to the eastern Great Lakes of Erie and Ontario and an offshoot shows up along the panhandle of Alaska (e.g. Juneau).

Europe and Hardiness Zone 6

Plant Hardiness Zone 6 in Europe.  Image courtesy of Davis Landscape Architects, modified by James Gibson.

Plant hardiness zone 6 in Europe. Image courtesy of Davis Landscape Architects, modified by James Gibson.

Zone 6 generally forms a north-south pattern with its center in Poland.

To the north it stretches along the Baltic Sea coast up to Estonia, then west to include Stockholm, Sweden, and Oslo, Norway.

From the center in Poland, the zone to the south stretches as a mass from eastern Germany and Switzerland down to Albania and western Bulgaria.

Significant Zone 6 Regions in East Asia

An area of zone 6 runs from north of Beijing in a south-western belt to north of Lhasa, plus a mass in western China on the border with Kazakhstan.

The zone also becomes more significant in Japan and Korea.

The patterns of plant hardiness zone four in China, Japan and Korea. Image courtesy of Davis Landscape Architects, modified by James Gibson

The patterns of plant hardiness zone 6 in China, Japan and Korea. Image courtesy of Davis Landscape Architects, modified by James Gibson

Plant Options for Gardeners

According to PBS’s The Victory Garden, the following plants grow well within hardiness zone 6:

  • American holly (Ilex opaca)
  • California privet (Ligustrum ovalifolium)
  • Common boxwood (Buxus sempervirens)
  • English ivy (Hedera helix)
  • Japanese maple (Acer palmatum)
  • Winter creeper (Euonymus follunei 

Asian Plants Thrive in Low Temperatures

The low temperatures experienced in zone 6 encourages gardeners to carefully consider what plants work best in their zone, while still allowing many Asian-origin plants and others to not only survive, but thrive.

Zone Four: USDA Plant Hardiness World View

The major world concentrations of USDA plant hardiness zone 4. . Image by James Gibson.

The major world concentrations of USDA plant hardiness zone 4. Image by James Gibson.

If you live around cities such as Anchorage, Alaska; Sherbrooke, Quebec; Ottawa, Ontario; Calgary, Alberta; Prince George, British Columbia; Butte, Montana; Bismarck, North Dakota; Casper, Wyoming; Minneapolis, Minnesota; Watertown, New York; Burlington, Vermont; Moscow, Russia; or Harbin, China; your plant hardiness zone is 4.

This means your average minimum winter temperatures are between -20°F and -30°F (-43.5 to -28.9 C).

Just remember, however, that on January 15th, 2009, as reported by Heather Adams, the temperature at the Bismarck Airport was -44°F, breaking the -36°F record set January 15, 1971.

Ideal Plants in Zone 4

According to PBS’s The Victory Garden, USDA plant hardiness zone 4 is ideally suited to plants of East Asian origin. The zone straddles the 45°N zone unless significantly impacted by water or elevation influences (e.g. Murmansk area of arctic Russia, 69° N; Anchorage, Alaska, 61° N).

The zone is restricted to the northern hemisphere because of its association with very cold and stormy interior continental type climates. Continental climates are not found in the Southern Hemisphere due to the absence of a land mass large enough and far enough away from the oceans and its currents to generate this effect.

What are Hardiness Zones?

Hardiness zones are defined geographic regions, most commonly based on USDA criteria, that support specific plants, flowers, and trees. They usually define a minimum range of temperature that a plant or tree can survive safely in that zone.

If possible it is advisable to consult other planting-related maps such as first and last frost dates, and heat zones.

Canada’s Zone Four Regions

In Canada USDA zone 4 dominates the southern interior of British Columbia, spots south-western Alberta, and crosses north-central Ontario from Thunder Bay to Ottawa and up the St. Lawrence River estuary into the Martime provinces.

Agriculture and Agri-Food Canada (AAFC) lists Peegee hydrangea (Hydrangea paniculata ‘Grandiflora’), Bouquet Blanc mock-orange (Philadelphus ‘Bouquet Blanc’), and Japanese yew (Taxus cuspidata) as shrubs indicative of this zone.

Zone Four Regions in the United States

The hardiest zone 4 takes a wide swath from below the Canadian border at Alberta, across the middle of Montana and the Dakotas, stretching from the Rockies to lower Wisconsin where it sweeps away from the cold of Lake Superior. Farther south it stretches as far down as Colorado in the west.

The patterns of plant hardiness Zone 4 in USA. Image courtesy of the USDA, modified by James Gibson

The patterns of plant hardiness zone 4 in USA. Image courtesy of the USDA, modified by James Gibson

With the water influence of the oceans, the zone stretches into upper New England beyond Lake Ontario and along the southern and western shores of Alaska.

Russia, Kazakhstan and Hardiness Zone Four

A large portion of Russia west of the Urals in a belt running down through Moscow, lies under the influence of the Atlantic Ocean and within climatic Zone 4. In addition, severe winters determine a Zone 4 in the areas extending southeast below the south end of the Urals into Kazakhstan and toward Lake Balkhash near the northern Chinese border.

The patterns of plant hardiness zone 4 in Russia and Kazakhstan. Image courtesy of Davis Landscape Architects.

The patterns of plant hardiness zone 4 in Russia and Kazakhstan. Image courtesy of Davis Landscape Architects, used with permission, all rights reserved.

Zone Four Patterns in China

Plant hardiness zone 4 takes a wide 45°N swath from just above North Korea, through the city of Harbin and on to the Gobi Desert, before reaching the border with Kazakhstan. Due to the elevation influence of the Himalayas, a belt also forms farther south across northern Tibet at 35°N.

Plant Options for Gardeners

According to PBS’s The Victory Garden, the following plants grow well within hardiness zone 4:

  • Amur River privet (Ligustrum amurense)
  • Chinese juniper (Juniperus chinensis)
  • Sugar maple (Acer saccharum)
  • Panicle hydrangea (Hydrangea paniculata)
  • Vanhouffe spirea (Spiraea x vanhouttei)
  • Virginia creeper (Parthenocissus quinquefolia)

Asian Plants Thrive in Low Temperatures

The low temperatures experienced in zone 4 encourages gardeners to carefully consider what plants work best in their zone, while still allowing many Asian-origin plants and others to not only survive, but thrive.