MASTER GARDENERS: Are there microclimates in your garden?
A microclimate is defined as the climate of a small area that differs from the surrounding region.
As gardeners we all check the hardiness zone before buying new plants and we keep tabs on frost dates to make sure the plants survive. There is another important factor to consider before planting. Are there microclimates in your yard?
What are microclimates and what causes them? A microclimate is defined as the climate of a small area that differs from the surrounding region. The area may be as small as a part of your yard or as large as a city. Large scale microclimates may be caused by elevation changes. Temperatures decrease as elevation increases, but on calm, clear nights heavier cold air sinks into valleys making them colder than surrounding areas. Frost may occur in the valley while the area around it is frost free.
Water also can create microclimates since it tends to warm and cool more slowly than the surrounding land moderating temperatures. Since I live on water I have learned that in the fall the temperature has to be at about 28 degrees in order for my plants to freeze. The bonus is a bit longer growing season.
Cities create their own manmade microclimates. Concrete and asphalt absorb heat during the day and radiate that heat at night. On calm nights temperatures can be as much as 10 degrees warmer than the surrounding area.
All of those situations can cause microclimates in your yard on a smaller scale. You may have already observed low spots in your garden that freeze before the rest of the garden. Foundation plantings benefit from the heat loss from the home creating a small microclimate. Planting next to paved driveways and sidewalks creates a slightly warmer climate.
You can create a microclimate in your garden that will allow you to grow plants outside your zone. We are in zone 3 in our area and growing plants hardy to zone 4 is usually not too risky, but if you were able to create a small microclimate, growing zone 5 plants could be possible.
Growing out of zone plants would be best done next to the house to have access to the radiant heat at night. This would be especially helpful if the planting was done with southern exposure to protect from the northerly winds. Fences and shrubs can also protect from winds and therefore help to moderate temperatures. Any type of covering can protect plants from cold temperatures.
Sun exposure, the slope of the land, and the direction the garden faces all influence temperature. South facing slopes tend to be warmer and drier while north facing land is cooler and oftentimes wetter. Shade, of course, causes a cooler environment and as a result soil temperatures rise more slowly in spring delaying seed planting.
When you identify microclimates on your property, you can choose plants that are best suited for each particular spot. You can also choose to create a microclimate in your own yard. Making an area that's able to grow more unique plants can be an adventure.
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