What is A Hardiness Zone – Does It Matter?
If you’ve spent any time in online gardening communities, you might have seen references to what “zone” someone is gardening in. Or you might have been told you’re in Zone 7a or 5b. If you’ve never gardened before, it can seem like these folks are speaking a different language. What do these zones mean and does it matter for your garden?
What is a Hardiness Zone?
The United States Department of Agriculture (USDA) has published a map of “Hardiness Zones” based on the average annual extreme minimum temperature across the U.S. The map was originally published in 1960 and has been updated in 1990, 2012, and 2023. There are 13 zones which represent 10 degree bands of minimum temperatures. Each zone is broken down into 5 degree half-zones which are given an (a) or (b) addition.
The zones range from the coldest (Zone 1a has -60 degrees F as the average annual extreme minimum temperature) to warmest (Zone 13b has 70 degrees F).
You can use the USDA hardiness zone to figure out which perennial plants would survive through the winter in your location. Seed companies also sometimes reference hardiness zone when they make recommendations for different seed varieties in catalogs or online shops.
How Do I Find My Zone?
The easiest way to find your USDA hardiness zone is to use the interactive map. You can zoom in to your region or enter your zip code to find your zone.
Does My Hardiness Zone Matter?
Your hardiness zone matters much more for perennial plants, shrubs, and trees than for annual garden plants. If you are hoping for your perennial plants to survive through the winter and come back in the spring, then you need to make sure you are planting varieties that match your zone. For example, if you are planting an apple tree and you live in zone 6a, any tree that is rated for zones 1-5 would work, or 6a, but if the tree is zone 6b or higher, it might not make it.
What if you really want to grow something that isn’t rated for your zone? There are things you can do to protect your more delicate plants. Some ideas include:
- Planting in a container and bringing it inside each winter.
- For plants that die back each year, heavy mulch can protect the roots.
- Planting in a sheltered area out of the wind can create a micro-climate that might be warmer than out in the open.
- Planting in a cold frame or greenhouse.
If you are planting annual garden plants, your hardiness zone doesn’t matter as much. The length of your growing season – from your last frost in the spring to your first frost in the fall makes more of a difference than your zone. However, different parts of the country with the same zone can sometimes have similar growing seasons, so advice from gardeners with the same zone as you might work better in your garden.
Now you know what your zone is. You can throw that information around like an experienced gardener in the online forums.
But if you need help actually figuring out the planting dates that matter for your garden, check out How Do You Know When to Plant.
Looking for help keeping your plants healthy and strong in whatever zone you’re in? Check out Mission Healthy Plants, my 3-day course on basic plant care to get your garden thriving.
