The United States boasts a diverse landscape. Understanding planting zones as well as microclimates becomes crucial in successful gardening and maintaining a landscape in which plants thrive.
Planting Zone Map
If you want to easily find your specific planting zone, click here and simply type in your zip code.
What Are Planting Zones
Planting zones, also known as hardiness zones, are regions categorized based on their average annual minimum temperature. These zones help gardeners and growers identify plants most likely to survive the climatic conditions of a particular area. The United States Department of Agriculture (USDA) created the USDA Plant Hardiness Zone Map, dividing the country into numbered zones ranging from 1 (coldest) to 13 (warmest). Each zone represents a 10°F difference in average minimum temperature. Each zone is further broken down into an A and B category representing 5 degree increments. So for example, Zone 5a has a low temperature range of -20 to -15 degrees (f), and Zone 5b has a low temperature range of -15 to -10 degrees (f).
How Are Planting Zones Determined
Planting zones are primarily determined base on temperature extremes. Data collected over multiple years regarding the lowest average temperature during the winter helps delineate these zones.
Shifts In Planting Zones
Planting zones are not static; they evolve due to various environmental factors, as well as advances in reporting. Recently, in 2023 the plant hardiness zone map received its first update since 2012. These changes reflected warmer minimum temperatures in many areas, leading to zone adjustments. Nearly half the country entered into a warmer zone.
People may be quick to attribute the warmer shift in zones to global warming, but it’s more likely that recent changes in data collection have led to the shift in zones. The amount of weather stations used to collect data has nearly doubled since 2012. And the location of these stations are particularly interesting. A lot of these new stations are in mountain zones where during the winter, warmer air hangs high, while cooler air sits in the valleys.
The USDA said the following regarding the explanation for the changes in the recent planting zone map:
“Temperature updates to plant hardiness zones are not necessarily reflective of global climate change because of the highly variable nature of the extreme minimum temperature of the year, as well as the use of increasingly sophisticated mapping methods and the inclusion of data from more weather stations. Consequently, map developers involved in the project cautioned against attributing temperature updates made to some zones as reliable and accurate indicators of global climate change (which is usually based on trends in overall average temperatures recorded over long time periods).” (USDA, Nov 15, 2023)
While planting zones provide a general guideline, microclimates present nuanced variations within a specific area. Microclimates are small-scale areas with distinct environmental conditions differing from the surrounding region. Factors like proximity to buildings, slopes, bodies of water, or even vegetation cover can create microclimates. These variations in temperature, humidity, and wind patterns significantly impact the success of plants within your landscape.
Effects of Microclimates on Plants
Understanding microclimates is crucial for successful gardening. A plant at your local garden center might fall within your specific hardiness zone, but when planted in your yard the microclimate may have a greater influence. Utilizing this knowledge allows gardeners to strategically place plants where they can thrive despite the general zone limitations.
For instance, a south-facing wall may create a warmer microclimate, enabling the growth of plants that might not typically survive in the region’s average conditions. Or, a fully exposed plant at the highest elevation of your landscape may endure colder temps and stronger winds than what’s typical of your growing zone.
Understanding planting zones, their changes over time, and the influence of microclimates is important when choosing plants for your garden and landscape. While planting zones provide a foundational understanding, recognizing and harnessing the potential of microclimates increases the likelihood of plants thriving.
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