USDA Hardiness Zones: More of a guideline than a rule

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Updated Aug 5, 2021
Ponds can be used as heat traps to help create microclimates around your customer’s landscape. Photo: Sam Felder/FlickrPonds can be used as heat traps to help create microclimates around your customer’s landscape.
Photo: Sam Felder/Flickr

It’s true that the climate in which you live greatly determines the types of plants that thrive in the area, but that doesn’t mean it’s impossible to have plants of all kinds present in a landscape.

United States Department of Agriculture (USDA) hardiness zones are nothing new in the landscaping world, but just because a plant is “not supposed to grow here” shouldn’t keep you from looking into options outside of your USDA zone.

By learning to take advantage of natural elements, you can design microclimates which will allow you to significantly increase the diversity of plants that grow in a region.

If you have customers who ask for exotic plants in snow-prone areas, fear not. By learning more about microclimates, you may still be able to give your customers the oasis they crave.

What are microclimates?

Microclimates are spaces in landscapes where the climate and temperature are significantly different than the immediate surroundings, and they can occur naturally or can be created.

Microclimates depend on the concentration of certain natural elements in specific places. For example, an area of a landscape that receives an ample amount of sun will be warmer than an area that doesn’t receive as much sunlight.

According to the Permaculture Research Institute, on one acre parcel of land, the average temperature can vary up to 10 degrees Fahrenheit from one part of the land to the next because of the microclimates that exist.

One of the easiest ways to identify a microclimate is to pay close attention to the behavior of pets or farm animals. During times of high heat, animals will migrate to parts of the landscape with cooler temperatures and vice versa. Once the possible microclimates have been identified, begin collecting data and observations to determine more about it.

Growing zone myths

Regardless of the customer requests, many landscapers will not venture farther than their USDA hardiness zone will permit, but it’s not necessarily a number that’s set in stone.

According to the Permaculture Research Institute, diversity is what allows the greatest amount of resiliency in any sort of ecosystem; the more diverse a system is, the better the chance it has to be sustainable and yield good quality plants.

In any given growing zone, there are many different situations that can affect the region’s exact climate. While climate and growing zones offer a general picture of where you’re located, they don’t always give an accurate representation of what all can actually grow in certain areas.

How to create microclimates

Microclimates are made by harnessing elements and concentrating the energy they bring into a certain area. There are a number of different elements that can be used to create a microclimate, but three of the most well-known and powerful are the wind, sun and water.

The creation of a microclimate depends on the energy from the sun and requires landscapers to find different ways to collect the heat and light from the sun into one area. One effective and commonly used method is planting heat or sun traps behind a customer’s home.

For example, the sun falls to the southern sky during winter in the northern hemisphere. By planting a row of trees behind a customer’s home (on the northern side), the trees will capture the sun’s light once they’ve grown large enough. This will not only provide a cooler section of the landscape, it will also help reduce power bills for your customers.

Speaking of heat traps, water can also serve as a heat trap and as thermal masses. Ponds and lakes are typically darker colored and therefore absorb the heat from the sun. This absorbed heat not only warms the water, it also heats the surrounding landscape. If you place ponds around a landscape, areas of heat absorption are created and the land around those ponds will be much hotter than other areas around.

Even though the wind is constantly shifting, it generally comes from one certain direction. Once the direction is identified, windbreaks can be planted to block it. Windbreaks can be bushes or densely planted trees. By planting a few hedges or trees around your customer’s landscape, the overall temperature can either be lowered or increased, depending on the surrounding temperatures.

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