Plant hardiness zones—also known as planting zones or growing zones—help gardeners understand which plants can survive their region’s climate. Find out which planting zone you’re located in so that you can grow your best garden yet!
What Are Planting Zones?
When choosing perennial plants for your garden, it’s important to select varieties that can thrive year-round in your area, especially in regions where extreme winter temperatures are normal. Planting zones define, generally, which plants can survive winter in your area, and zones are typically listed in plant growing guides for reference.
The two most commonly referenced hardiness zone maps are those produced by the U.S. Department of Agriculture (USDA) and Natural Resources Canada (NRC). Different measures are used to create each country’s map, as explained below.
Zone maps are not absolute; if you find the information contradictory to your own experience, you may live in a microclimate. Soil, moisture, humidity, heat, wind, and other conditions also affect the viability of individual plants.
Find Your USDA Planting Zone
Considered the standard measure of plant hardiness, the USDA Plant Hardiness Zone Map is based on average annual minimum winter temperatures. The map is divided into thirteen distinct 10ºF zones, which are further divided into sub-zones of 5°F.
Check out an example image of the official USDA Plant Hardiness Zone Map below, then go to the USDA website to find out exactly which zone you live in!
Note: The USDA Plant Hardiness Zone Map was last updated in January of 2012, the first update since 1990. About half of the country was made a half-zone warmer on the map. According to the USDA, the scientists are using a different set of long range data and more sophisticated computers for a more accurate map, especially in challenging areas such as mountain zones, which may have been rated too cold or warm in prior iterations of the map. Learn more about the updated map here.
How to Use Your Planting Zone
Planting zones are most useful to gardeners growing perennial plants, since perennials are meant to live beyond just one growing season. Perennials need to be able to survive winter in your area, so it’s important to know how cold it typically gets in your area and whether a particular plant is hardy enough to survive those temperatures.
Perennial flowers, shrubs, and trees grow best when planted in the appropriate zone. You’ll find that winter damage occurs most often when plants are out of their range or “comfort zone.” When you choose plants for a garden or landscape, avoid selecting plants that are only marginally hardy for your region; that’s when you’ll see winter damage, poor growth, and a reduction in flowering.
Planting native species is a surefire way to achieve a stable garden. See our article on natural landscaping.
For annual plants, like most vegetables and some flowers, it’s far more important to pay attention to things like the length of your growing season and the typical dates of your first and last frosts. (See local frost dates here.) Because annuals are only meant to last the length of one growing season, planting zones don’t necessarily factor into the equation.
NRC Canadian Planting Zones Map
Unlike the USDA map, which is based only on minimum winter temperatures, the planting zones map produced by Natural Resources Canada considers a wider range of climatic variables, including maximum temperatures and the length of the frost-free period. However, the NRC also produce a map that shows plant hardiness zones for Canada based on the USDA extreme minimum temperature approach. Click here to see both Canadian planting zone maps.
Check out a simplified version of the official Natural Resources Canada Plant Hardiness Zone Map below, then go to the Natural Resources Canada website to find out which zone you live in!
Another key part of successful gardening is knowing when your frost dates are. Find your local frost dates here.
What are your thoughts on planting zones? Are they accurate? Let us know in the comments below!