How Plant Zones Work and How to Find Yours

When you’re at the garden center or shopping from an online nursery, a plant’s zone is always clearly marked on the plant tag, seed packet or online profile. These hardiness zones reflect the average minimum cold temperatures for an area and tell you whether the plant will survive the winter cold in your backyard. If your hardiness zone is within the plant’s range, the plant has passed the first test for growing success.

For example, my Wisconsin home is in Zone 5a, where the average minimum winter temperature range is -20 to -15 degrees Fahrenheit. Although the temperatures rarely get that cold (while some years it may be colder), it’s crucial that I buy plants that tolerate deep winter chills. When you push the limits of your zone, as many gardeners do, you risk failure when temperatures drop below the limits that a plant can endure. (Read more! Gardening Basics You Should Know to Keep Plants Healthy)

How to Find Your Plant Zone

Take a look at the USDA’s Plant Hardiness Zone Map online. Identify your location, match the color in your region with the key next to the map, and voila: that’s your number. You may want to choose plants that are one zone hardier than your region, just for a bit of added insurance. (If you’re in Canada, you can find your Plant Hardiness Zone Map here.)

Each of the 13 zones in the U.S. represents a 10-degree Fahrenheit band of minimum winter temperatures. Those areas are then subdivided into 5-degree segments (that’s why you may see “a” or “b”) to more precisely represent that area within each section. You’ll also notice that the lower the number, the colder the winter temperatures.

As you look at the map, you may notice islands of warmer or colder zones within the band of another. Large bodies of water, urban heat islands (areas that are warmer than rural areas because of human activity), mountains and valleys influence the surrounding climates and growing conditions. These microclimates also exist within your landscape. Sheltered areas may allow you to grow less-hardy plants, while more-exposed areas require tougher specimens. (Read more! 6 Common Plant Problems and How to Solve Them)

Use Plant Zones for Garden Success

For absolute success, take it one step further. Make sure the plants you choose are suited to all the growing conditions in your landscape. Once again, check the tag, seed packet or plant profile to know for a fact that your selection will receive the sunlight, soil type and moisture it needs to thrive. Then make sure there is sufficient space for it to reach full size; it’s amazing how fast those little plants grow into large specimens. All these factors together mean a healthy, thriving and beneficial backyard. (Read more! 12 Easy Ways to Take Your Garden to the Next Level)