What’s your Hardiness Zone?

And does it matter?

Your USDA Hardiness Zone is a piece of gardening information which is really helpful to know — but it isn’t the only piece of a very complicated puzzle. So learning about your zone is only one measure of whether a plant will do well in your area.

Ok. Let’s get started…

A gardening term you probably hear and see often is “your zone” or “your hardiness zone.” This is a good piece of information to know – but it has its limitations.

What is a hardiness zone?
The USDA has created a map of the US divided into hardiness zones. This tool was originally created to help farmers throughout the Midwest plan their crops, but it has been expanded to the entire horticultural trade.

The zones indicate the AVERAGE lowest temperature over a winter and are calculated using more than 20,000 temperature centers across the country. That’s a lot of data!

How do you know what zone you are in?
Consult the USDA Hardiness Zone tool where you can input your zipcode and see which zone you are in. It’s that simple! You can see what your average lowest temperature should be. And if you are

So I am technically in Zone 6 which means the lowest temperature on average that I can expect is -10℉. However, that's only an average. And in the last few years we have gotten down to -24℉. So you have to remember that this is an average.

Why are USDA zones important for gardeners?
USDA zones are crucial for choosing plants that are suited to your climate. By knowing your zone, you can select plants that are more likely to survive and thrive in your region, avoiding plant damage from extreme temperatures or unsuitable growing conditions.

Can I plant anything in my USDA zone?
Plants are often marked as "hardy to zone 4 or zone 6." But that is only part of the story with a plant. Those zones are averages, and plants often can't tolerate the colder ends of those averages.

Also hardiness zones don't take into account factors like rainfall, summer heat, altitude, and so many other factors that go into a plant's health. Nor do they account for the length of time at that lowest average temperature. There is a big difference between one night at -24℉ and several weeks with sustained low temperatures at -24℉.

So just because a plant is “hardy to zone 5” doesn’t mean it will necessarily thrive in YOUR zone 5. It’s just a starting point.

Hardiness Zones FAQs

No, USDA zones are based on minimum winter temperatures, not summer heat. While they are helpful for selecting plants that can survive winter, you should also consider heat tolerance and growing season length when choosing plants for hot climates.
Knowing your USDA zone helps you select plants that will thrive in your climate, allowing you to plan your garden with confidence. You can choose perennials, trees, shrubs, and even vegetables that are well-suited to your zone, ensuring a healthier, longer-lasting garden.
No, other countries have their own systems for determining growing zones. For example, the UK uses a different set of climate zones, and Canada has its own hardiness zone map. While they follow similar principles, the specific climate data may vary. Always check for the zone system specific to your country or region when planning your garden.
No, other countries have their own systems for determining growing zones. For example, the UK uses a different set of climate zones, and Canada has its own hardiness zone map. While they follow similar principles, the specific climate data may vary. Always check for the zone system specific to your country or region when planning your garden.

USDA Hardiness Zones Updated

I made this video for Botanical Interests to explain the changes in 2023 to the USDA maps — and what that means for gardeners.

When were the hardiness zones updated?
In 2023 the USDA issued a new map calculated on the previous 20 year averages — something they do every 20 years. More than half of the country shifted half of a zone. With climate change, this is to be expected. But averages can hide the extremes of weather patterns — which have become more extreme with climate change. They indicate a trend over time — not the highs and lows.

So what does that mean for us as gardeners?
Honestly, not much. For me, here on the Front Range in Colorado, I garden as if I am in Zone 4 – even though I am solidly in Zone 5|6. That's particularly true when I'm choosing perennials that aren't native to my area – like fruit trees and roses. I want plants that will withstand the extremes of cold that we may sustain knowing that in an average winter that won't happen.

And of course, this only applies to perennial plants. Annuals could not care less what zone they are in!

Happy gardening!