Find Your USDA Plant Hardiness Zone
If you’ve ever picked up a packet of seeds or looked at plant tags at the nursery, you’ve likely seen a reference to the USDA Hardiness Zones Map, also called gardening zones or planting zones. Understanding the USDA Plant Hardiness Zone Map can help you choose the best plants for your area, ensuring they survive and thrive in your local climate.
But many gardeners don’t really understand what these gardening zones mean and that can lead to some frustration, especially for the spring and summer garden. Let’s chat about what gardening zones are and how to use them in your garden planning.
If you don’t know what gardening zone you’re in, go ahead and type your zip code into the search box at the top of the interactive map above and tap search to find out. Be sure to write that in your garden planner.
What is Plant Hardiness?
Plant hardiness refers to how well a plant can survive winter temperatures. If a plant can survive without protection it’s hardy or cold hardy for that climate. The plant may go dormant but when spring comes it revives, we call these plants perennials.
If a plant isn’t cold hardy for your area, it will die over the winter and not revive. These plants are called annuals.
One isn’t better than the other, they’re just different. And there are many plants that are grown as perennials in some climates and then as annuals in other climates. This is where knowing your hardiness zone can help you make good choices and manage gardening expectations.
What Are USDA Hardiness Zones?
When I first started gardening I had no idea about gardening zones, well, I had heard about them and I could see on a plant tag that the plant was “hardy” to zone 9 (which is my zone) but what did that mean?
In 1960, the United States Department of Agriculture (USDA) created the USDA Hardiness Zones and illustrated map for North America to serve as a guide for gardeners and growers. These zones are based on the average annual extreme minimum temperature of a given location.
The zones are divided into 10-degree F increments and then each zone is subdivided into 5-degree F increments. There are 13 zones and each zone has an “a” and “b” subzone.
Since gardening zones are based on an average annual extreme minimum temperature, knowing your zone will help you understand what plants will survive the winter temperatures without protection in your area.
What’s New in the USDA Zone Map?
The USDA Plant Hardiness zone map was updated in 1965, 1990, 2012 and most recently in 2023. If you were a gardener who spent anytime online in 2023 you saw people going a little crazy because they were now in a different zone. But here’s the deal, the new map shift didn’t put them in a different zone – the weather did.
Also, most of the shifts were from one subzone to another, there wasn’t wild leaps across the map. And honestly, those small (less than 5 degree) differences aren’t something to get riled up about. It’s not going to really matter.
The plant hardiness zone map reflects updated data from recent years, which gives gardeners a better understanding of their local climate. Environmental factors such as extreme winter temperatures, extreme lows, and changes in average lowest temperature contribute to the shifts in zone boundaries. Also, Puerto Rico and other U.S. territories are now included in the updated map.
But at the end of the day, these are just averages. The actual weather conditions from year to year can be colder or warmer than the previous ones.
How to Use Gardening Zones
I think the first thing to know is that just because two areas are in the same growing zone, don’t assume they’re exactly the same. Just because rhubarb may grow well as a perennial in Coastal Oregon which is zone 9, it won’t in the Texas Gulf Coast, also zone 9. Texas summers are just too hot for the rhubarb to survive as a perennial but it can be grown as an annual.
As mentioned above knowing your gardening zone will help you with plant selection and if a plant can be grown as a perennial or annual. For instance, oregano can be grown as an perennial in zones 4-10, but won’t make it through the winter in zone 3 without protection.
As a general rule, plants will be hardy in any zones warmer than the ones listed. For instance, if a plant is hardy in zone 8 it will also survive a zone 9 winter. Now, that doesn’t mean that it won’t die from heat in the summer, so it might still not be a perennial in zone 9 (see rhubarb example above), but it will survive the winter.
Some plants need a certain minimum temperature during the winter in order to revive or fruit in the spring, so choosing plants that are hardy in your planting zone is key for being able to grow these plants.
Also, there may be small areas on your property that will have different temperatures than the rest of your property. For instance, some plants that might not survive if planted on the north side of the house, might do just fine on the south side of the house.
Lastly, it’s important to remember that one gardening zone isn’t “better” than another. Each zone has it’s pros and cons. I can grow citrus in zone 9 along the Texas Gulf Coast but not apples. When you understand not only your gardening zone but also your local climate, you’ll be able to make the most of your gardening zone.
Other Factors For Garden Success
As you probably have guessed, knowing the average lowest temperatures for your area isn’t the only thing you need to know to have a successful garden. Here are a few more factors to consider.
Frost Dates: A growing season is usually considered the days between the average last frost date (in the spring) and the average first frost date (in the fall). That doesn’t mean you can’t grow plants in between the frost dates, but if they aren’t cold hardy, they’ll need protection. Once you know your frost dates, you’ll be better prepared to make a planting schedule. Be sure to include some succession planting in your schedule.
Number of Chill Hours: Many fruit trees need a certain number of chill hours (hours under 40 degrees F) in order to bloom in the spring. When you’re planning your backyard orchard, be sure to check the chill hour requirements of the fruit trees. If you plant a tree that requires more chill hours than your climate gests you’ll end up with a tree that doesn’t fruit. If you buy a tree that requires fewer chill hours than you get, you run the risk of the tree blooming before your last frost.
Well-Drained Soil: One of the most important factors in your garden is healthy soil. Before spending a bunch of money on plants and seeds, be sure that you have a plan to feed them by building healthy soil.
Water: Do you have a good water supply for your garden or orchard? In the heat of the summer, dragging water hoses all over the yard trying to water everything will get tiring. When you plant new fruit trees or expand the garden, make sure you can maintain the watering.
Summer Temperatures: As mentioned before heat can affect whether a plant is an annual or perennial, just like the lowest winter temperatures can. It’s one thing to have a couple of days a year that reach 95 or 100 degrees F, many plants can survive that with a little extra water and shade cloth. But most won’t survive if you have a 100 days of extremely high temperatures.
Sun and Shade Requirements: Sun and shade can also create micro climates on your property. If you have a bunch of shade on your property you might not be able to grow some plants that require full sun.
Keeping Records: One of the best things you can do for your garden is to keep records. It doesn’t have to be fancy, just keep records of what you grow and how they did. You don’t need to keep weather records of each day but if something unusual happens, it’s a good idea to jot it down. Over time, these records will help you understand your specific climate.
By using the USDA zone map and understanding your local climate, you can create a thriving garden filled with native species and cold-hardy plants that withstand the temperature range of your particular area. Whether you’re growing vegetables, flowers, or perennial plants, knowing your gardening zone is one of the most important tools for success!
