Hardiness Zones Explained

Learning More About Hardiness Zones

U.S. Plant Hardiness Zone Map
U.S. Plant Hardiness Zone Map. Photo courtesy of U.S. Department of Agriculture

Gardening is such an intriguing practice, somewhere between an art and a science. Countless generations of wisdom and experience have been passed along, combining folk wisdom with proven science to result in carefully tended, productive backyard gardens. If you’ve been fortunate enough to come from a gardening family, you have that one trick that helps you know when to plant something or what does particularly well in your area.

For those of us who don’t have gardening in our DNA, we have to rely more on tools than timeless wisdom, like the map of hardiness zones. Sometimes, the map of zones can be invaluable. Other times, confusing. When you learn what the map was intended to do and how it applies to your garden, though, it can save you a lot of trial and error.

How the Zones Are Divided

The idea behind the map of hardiness zones is that, in light of our access to limitless varieties of plants, we need a quick way to know what will grow well in our respective areas. Without zones, a seed company would not be able to easily indicate the ideal climate, leaving us to know before we buy or close our eyes and hope.

The USDA hardiness zones are most commonly used, though there are other divisions, as well. Each zone is indicated by the lowest average temperature that region reaches in the winter time. You can look at the maps for a general idea of where you are; you can find where you are exactly based on​ your zip code, or you can determine your average winter temperatures and purchase plants and seeds for the corresponding zone.

So, you can use the zones as generically or specifically as you’d like.

Because it is based on coldest annual temperatures, US zones begin at the very northern part of Alaska as 1, moving into higher digits the further south you go. The division lines aren’t straight, thanks to varied weather patterns due to wind currents, terrain, and other factors that affect the weather.

Using Zones in Your Garden Plan

Once you know what your garden zone is, you can use it to help with your garden plan. First, know that buying seeds and plants that do well in your zone does not guarantee that they will do well in your garden. Many other factors – like soil health, sunlight, and local nuances – come into play. Hardiness zones are just one piece of the puzzle.

Not only that, but hardiness zones apply to perennials, shrubs, and trees, that would need to overwinter. The map, remember, is based on winter temperatures. If a plant is hardy to a certain zone, it means that it will stand up to an average winter. So for annuals that you don’t expect to return, the zone means very little.

Note that zones are really more like guidelines. Just as an appropriately zoned plant won’t automatically do well in your yard, the intricacies of your particular garden can help bend the “rules” of zones so that a less than ideal plant thrives anyway.

Finding Your Zone

You can find your general zone by pinpointing it on a USDA Hardiness Zone map, or you can use a web tool to find it more specifically. The USDA website has a tool where you input your zip code to find your exact spot on the map.

In addition to your hardiness zone, it’s always beneficial to reach out to local gardeners or nurseries and your nearest extension office.

They know your region and community well and should be able to help with any quirks that fall outside of the realm of average temperatures.