There are two related questions I get from new gardeners: “What is a planting zone?” and “What planting zone do I live in?” These questions arise because whenever you go to buy a plant, whether it’s online through a seed catalog or at a garden center, the plant description will include information on the planting zones where the plant can be grown.
This week, I’ll do my best to dispel some of the confusion around planting zones. I’ll define planting zones, discuss how to figure out what planting zone you live in, and provide links to maps showing planting zones in the United States and Canada.
What is a Planting Zone?
A planting zone, better known as a United States Department of Agriculture (USDA) Plant Hardiness Zone, is a geographic area determined by average winter temperatures. Basically, how cold does it get?
For each of the 11 different planting zones in the United States, there is a 10 degrees Fahrenheit difference between one planting zone and the zone adjacent to it. Planting Zone 1, in Alaska, is the coldest, and planting Zone 11, in Hawaii, is the warmest.
For gardeners and farmers, planting zones provide a guide for what plants grow well in certain areas. It comes down to not only how cold it gets, but whether a particular plant will be hardy enough to survive those cold temperatures.
In the plant descriptions provided by nurseries, you should always see information about the planting zones in the United States where the plant can be grown. For example, let’s say you were interested in planting Heritage raspberries. Whether you purchase the plants online or in a garden center, you would see that Heritage raspberries grow well in USDA Plant Hardiness Zones 4 to 9.
More Confusion: What’s a Sunset Climate Zone?
I don’t want to make things complicated, but if you live in the western United States, you’ve probably also been confused by the Sunset climate zones. The Sunset climate zones and USDA Plant Hardiness Zones do not always match up.
These planting zones were established by Sunset Magazine and have been around for the past 40 years. The 24 Sunset climate zones are much more specific and are based on not only average low temperatures, but rainfall, the length of the growing season, humidity, and average summer high temperatures as well.
Because of the zones’ specificity, most garden centers in the western United States use Sunset climate zones on their plant tags. If you live in the West, it’s best to know which Sunset climate zone you live in. However, it is still important to know what USDA planting zone you live in because, if you order plants from online garden catalogs in the Midwest or eastern United States, they will use the USDA Plant Hardiness Zones in their plants’ descriptions.
Thoroughly confused yet? I know.
What Planting Zone do I Live In?
Ok, so you’re standing in the nursery and the tag on the plant you’re thinking about buying says it grows well in zones 4 to 9. What does that mean? You’re probably asking yourself, “What planting zone do I live in?” This is where a little garden research before you venture out to buy plants can really help you.
But, let’s back up for a second and take the pressure off. First of all, it’s important to know that you don’t have to be a slave to planting zones and follow them precisely. The planting zones for the United States are a guide after all. Thankfully, there is some wiggle room, and, of course, some unpredictability when dealing with nature.
Let’s say you live in USDA Plant Hardiness Zone 3, but you don’t know that. You haven’t done your homework. It’s possible that you could find a plant at the garden center that does well in planting zones 4 to 9. It’s also possible that for the first two winters you have that plant in your garden, it could grow beautifully; maybe you have a mild winter, maybe it’s planted in a protected spot in your garden, or maybe the plant is particularly strong for its species. Whatever the reason, your zone 4 to 9 plant survives in your zone 3 garden.
Then, during the third winter, your plant dies. This happens, and it’s not the worst thing in the world. In fact, in colder climates, many of the plants sold as colorful, summer, container plants are, in fact, herbaceous perennials that thrive year-round in warmer climates. Yes, it’s money wasted, but it’s not the end of the world.
But you’re still asking, “What planting zone do I live in?”
Well, folks, that’s why there are maps.
Maps of Planting Zones in the United States and Canada
Luckily, planting zones in the United States can be found through the USDA and Sunset Magazine. You’ll see that planting zones on the USDA Plant Hardiness maps are broken down further into “a” and “b” zones with differences of 5 degrees Fahrenheit between them. A similar map of the plant hardiness zones in Canada is also available.
The Sunset climate zones can be found on their website and differ slightly from the USDA planting zones. According to Sunset, Seattle is in Sunset climate zone 5, but according to the USDA, Seattle is in USDA Plant Hardiness Zone 8b.
Clear as mud? As baffling as it may seem, don’t worry about it. The bottom line is: If you live in the western United States, use the Sunset climate zones. If you’re in the Midwest or the eastern United States, stick to the USDA plant hardiness zones.
Now that you know what planting zone you live in, go plant something.