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Utilizing Microclimates For More Diverse Gardening

To establish a more diverse, efficient garden, many gardeners are turning to microclimates for assistance. Microclimates are small areas, usually from a few feet to a couple miles across, that have different conditions from the surrounding area. These isolated pockets may differ in temperature, moisture, wind, or protection from frost and can be found in every garden in one form or another.

Microclimates are influenced by several factors, ranging from bodies of water to a picket fence. By taking advantage of the microclimates, gardeners can plant more effectively, help expand the growing season, and help plants that are marginal to the climate thrive.

Understanding Microclimates

Although the term “microclimate” may be new to some, most gardeners already use microclimates in their garden planning. We know to plant the warmth and sun-loving plants on the south side of the house, for example, and understand that shade and water-loving plants would prefer to grow underneath a tree or in a northern exposure.

To fully understand and take advantage of these microclimates in your garden, it’s important to also understand your region’s overall climate zone.

The USDA Climate Zones

Our country’s standard for determining climate zones is maintained by the USDA, which defines each region’s zone by determining low winter temperatures in a given area. If you haven’t already, review the USDA’s Plant Hardiness Zone Map to see where your region falls. This will give you an idea of which plant hardiness zones your microclimates may fall under. Your region may be Zone 6, for example, but a low-lying, shady microclimate on your property may be more like a Zone 5.

Sunset Climate Zones

An alternative climate zone system is the Sunset Climate Zone Guide, which covers the entire Western U.S. Unlike the USDA system, Sunset goes into much more detail. Sunset also addresses a common weakness in the USDA Zone definitions: plant growth is affected by more than just winter-low temperatures. Other factors, including soil composition, altitude, latitude, precipitation, and sunlight, play a role in a plan’s ability to thrive, and the Sunset climate zones were defined to take these into account. The biggest problem with this system, of course, is that a similar climate zone map isn’t yet available for the Eastern U.S.

Microclimate Factors

Microclimates can range in size from anywhere between several miles to only a few feet across and can be affected by both large weather patterns and localized warm and cold spots. Other factors, including precipitation, wind, and soil type, can also determine a microclimate.

Large-Scale Microclimates

Altitude: Gardens located at high elevations experience different growing conditions than surrounding low-altitude areas. The thinner atmosphere at high-altitudes means longer and colder winters, intense sunlight, dry air, and large temperature swings between day and night. Some plants manage to take these harsher conditions in stride, but others may struggle.

Valleys, Peaks, and Other Landscape Features: Unique landscape features, including canyons, valleys, floodplains, and cliffs, can have a profound influence on microclimates. Their topography can affect a garden’s exposure to severe weather and determine unique soil conditions. Cliffs and canyons can also severely limit a garden’s access to sunlight, while mountainsides can experience more precipitation.

Open Water: Open bodies of water such as lakes, swamps, and oceans influence microclimates by moderating the temperatures along adjacent land. Temperatures along coasts tend to be milder than further inland and are less prone to dropping into late or early season frosts.

Urban Areas: The large expanses of concrete and lack of green cover in today’s urban areas means that the sun’s warm rays are absorbed and then slowly released over a wide area. While this can mean milder winter temperatures, it can also mean scorching summer days. Cities may be an entire USDA zone warmer than the surrounding rural area.

Small-Scale Microclimates

Slopes: The slopes of a hillside influence microclimates by increasing drainage, offering more or less sun, and exposing plants to more or less wind, depending on exposure. In addition, slopes may have a “thermal belt,” which is the halfway point that stretches around a hillside. The ground in these thermal belts is somewhat warmer than the ground both at the crest of the hill, which is exposed to cold wind, and down below, where cool air pools.

Courtyards: Protected from the wind and often surrounded by heat-absorbent walls, courtyards are another example of a small garden microclimate. Stucco and brick walls absorb the sun’s warmth and slowly release the heat throughout the night, while simultaneously sheltering the garden inside from high wind. Plants that are marginal to your overall climate zone are more likely to thrive when planted on the south end of a sunny courtyard.

Walls, Gravel, or Sidewalks: The ground surrounding gravel or concrete walkways is likely warmer than the surrounding area. Like walls, concrete and gravel surfaces absorb and slowly release the sun’s heat. Large concrete or asphalt surfaces, such as roads and patios, may also drain rainwater downslope, providing more water to the plants that grow there.

Aspect: The direction a garden bed faces is a huge influence on the microclimate, as many gardeners are already aware. Areas facing south get more light and warmth, while north-facing areas stay cool and shady. Also, areas facing east often experience less heat than areas facing west, which often experience the hot afternoon sun. These aspects are emphasized by slopes and by barriers that can trap and reflect heat. Keep in mind though that sun exposures change somewhat throughout the year, depending on latitude, and so can microclimates.

Frost Pockets: Cold air sometimes collects behind walls, fences, and other barriers and can be made worse if the barrier is at the bottom of a slope. Plants located in frost pockets are more likely to experience damaging early and late frosts. This is especially problematic for early season flowers. You can break up a frost pocket by making gaps in the wall or fence to allow the cold air to flow away downslope.

Benefits

More Diversity

The conditions found in some microclimates can allow certain plants and varieties that grow outside the general climate zone to thrive. Careful plantings in microclimates, as well as the use of mulch and other insulation, allows gardeners to grow some of these plants more effectively and with less effort than in other areas of the garden.

Extended Growing Season

When combined with techniques like row covers or cold frames, microclimates can provide the conditions needed to grow vegetables earlier in spring and later into the autumn and winter months. And since most microclimates occur naturally, you don’t have to worry about maintaining them or putting in any extra work to take advantage of the added protection they offer to your cool-season vegetables.

Increased Vitality

Plants grown in the right area of the garden with microclimates in mind will be generally more healthy and resilient, as they will be spending less energy on survival and more energy in growth, fruit and flower production, and fighting off pests. These plants will be more likely to survive frost or drought and will also recover more quickly from transplanting or other stresses.

Potential Drawbacks

Fickle and in Need of Pampering

Planting something outside of your climate zone, even in a sheltered microclimate, is in no way guaranteed to work. Some plants may need extra TLC such as frequent watering or feeding needs, and many will be more susceptible to pests. In addition, some fruiting and flowering plants may not flower or set fruit well if their environment is at all less than ideal, and they may even perform inconsistently from year to year. Do a bit of research first and see if you can find some varieties that are more suited to your climate.

The When, Not If, of an Overwhelmed Microclimate

The range of average high and low temperatures in a given climate zone are by no means constant. Any region can experience an unusually mild or harsh winter, and severe or just plain bizarre weather can occur at any time of the year. Just a couple years ago, a city in USDA Zone 7 with normal low temperatures in the 0°F range experienced a winter storm with temperatures that plummeted to 20° below zero. Needless to say, many of the more delicate plants and shrubs – even the ones in sheltered microclimates – died back drastically or never came back at all. Another cold event like this one may not happen again for years or even decades, but it’s likely to happen again at some point, and plants marginal to the climate will struggle to survive.

No matter what climate zone your garden is located, you can take advantage of the naturally occurring microclimates scattered around the landscape to create a more efficient and diverse garden. With only a little bit of extra effort (and a dash of luck from the weather), your family can enjoy longer growing seasons and more unique varieties of vegetables for years to come.

References:

https://www.sunset.com/garden/climate-zones/climate-zones-intro-us-map-00400000036421/

https://planthardiness.ars.usda.gov/PHZMWeb/

https://www.gardening.cornell.edu/weather/microcli.html

https://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=689

https://www.gardeningknowhow.com/gardening-how-to/how-to-make-a-microclimate.htm

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