Garden zones or plant hardiness zones are frequently mentioned in gardening. But, do you know what your zone is? Or, how to find it—and—most importantly—what it means for your garden? Let’s look how this information helps but why it does not give the full picture for gardeners.
About Plant Hardiness Zones
What is a plant zone or plant hardiness zone, and what does it mean for your garden?
Different parts of the world have different systems for measuring plant hardiness zones. The ones we’re discussing here are for the United States and Canada.
The plant hardiness zone map for the United States was developed by the United States Department of Agriculture and is fairly basic compared to the Canadian system which is more detailed.
The USDA Plant Hardiness Zones are based on minimum annual temperatures. Maximum temperatures are also a concern for plants, but not covered by this system.
The higher the number, the warmer your minimum temperature over the year.
Your hardiness zone by no means tells you everything you need to know for choosing plants but it is one important factor.
The same zone number (minimum temperatures) can be found in a range of different climates from dry to humid, sand to clay, and many more variances that play a role.
Ultimately plant choices should focus on non-invasive species suited to your zone and specific growing conditions. Bonus if you ensure the plant provides either food, nectar, or habitat to support biodiversity.
Find Your Frost Dates & Hardiness Zone
Average Frost Dates | Use this calculator at Almanac.com. Enter your city and state or province to find your first and last frost dates and number of frost-free days.
Ecoregion | Learn about the native plant and animal species and environmental conditions specific to your region to better understand why your garden choices matter.
Learn More: Understanding Frosts & Freezing For Gardeners
Hardiness Zones as a Starting Point
A range of appropriate zones are shown on the tags of just about any perennial or tree you’ll buy. But, as mentioned, there are some things to keep in mind about gardening zones.
First, your zones are general guidelines, not hard and fast rules.
There are a lot of factors that determine whether plants will survive or not.
The USDA maps rely only on minimum temperatures—is this plant likely to survive the cold of your winter?—but there are many other reasons that plants may not survive in your garden:
- too hot in the hottest months
- not enough rainfall
- short frost-free periods
- frost at the wrong time
- snow cover or lack of it— and many others
And, your garden—or even parts of your garden—may be different from the zone for your area, depending on elevation, exposure to sunlight and other factors.
Sometimes it’s hard to figure out exactly why, but there are micro-zones or micro-climates within gardens. Plus or minus a zone or even two isn’t uncommon.
If you have been gardening a while you may have noticed that hardiness zones change over time as well. Climates change, temperatures change. Your zone is probably not what it was 20 years ago or what it will be 20 years from now.
And, of course, what would be a perennial in a higher garden zone may still work fine as an annual in your garden. It won’t likely survive the winter, but you can enjoy it this year, and perhaps overwinter it indoors until spring.
So, as you can see, it’s helpful to know your plant hardiness zone as a starting point. Factors unique to your garden will further determine what thrives in your garden.
~Melissa the Empress of Dirt ♛
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