Understanding & Using the USDA Plant Hardiness Zone Map

Gardening, Houseplants, How To / By

Last Updated on March 15, 2022 by Admin

If you’ve spent some time around plants or gardening you’ve probably heart about the USDA Plant Hardiness Zone Map. But what is it exactly?

Well, it is basically a map that tells you about the different climates in different parts of the United States.

And by learning how to use it, you’ll be able to know what plants you should or should not be growing where you live.

In this article, I’ll explain everything you need to know about the USDA Plant Hardiness Zone Map and how to use it.

 

What are Plant Hardiness Zones?

The USDA Plant Hardiness Zone Map was devised by the United States Department of Agriculture (USDA). It was published to help gardeners understand the different weather conditions in their specific area.

That way, you’ll be able to choose the right plants best suited for the climate in your location.

It’s important to understand that each country or region will have its own plant hardiness zone map. That’s because each nation will have different weather prevailing over it.

And, in the case of the U.S., there are quite a few plant hardiness zone maps available.

But, let’s start with the most common ones.

Important Note: Before moving on, it’s important to understand that these maps are meant to be used as guides. That is, they’re not etched in stone. Also, they’re not perfect.

Why? Because:

  • Climates keep changing. All the things happening around us are causing the climate to shift over time.
  • The maps aren’t updated regularly. They’re not like your Facebook or Instagram feed that’s up to date. In fact, if you look at the maps above, you’ll see most of them are at least 5 years old or older.
  • There are microclimates. A microclimate is a specific climate for a small area that’s different from those surrounding it. The presence of buildings, mountains, bodies of water and other things can affect the climate in your neighborhood to make it different from houses that are just a few miles away.
  • The maps don’t take into consideration all the factors that affect plant growth. It simply focuses on one, the climate.

 

What Do The Plant Hardiness Zones Mean?

Simply put, the plant hardiness zone map is a guide that tells you which plants are most likely to survive the winter climate in your region.

Just as importantly, matching the right plant with your zone improves your chances of growing them successfully year in and year out.

So how does the plant hardiness zone map work?

Basically, it maps out an entire country. In the case of the USDA Plant Hardiness Zone Map, it shows you the United States.

Here, the entire U.S. is divided into 11 planting zones. Each of these zones is defined by their annual minimum temperature. As such, that’s the main criteria the map uses to divide one region from another.

Each 10-degree temperature difference identifies one region. In some cases, you’ll see one region divided into “a” and “b” sections. When that happens, the temperature difference between them is 5 degrees.

And, the map starts with the lowest zones (coldest) going up to the highest zones, which are the warmest.

For example,

  • Zone 3 plants are those that withstand minimum temperatures of -40 to -30 degrees Fahrenheit. If you look at the map, the states included in Zone 3 are those in the Midwest, including parts of Wisconsin, Minnesota and Montana. All of which experience very cold winters.
  • Zone 4 plants are those that can survive low temperatures of -30 to -20 degrees Fahrenheit. These include hydrangeas and crabapple trees. And, the map shows that zone 4 covers parts of Wyoming, North Dakota, Montana, New York, and others.

As you can see as the zones go up, the change in their temperature range moves by 10 degrees. The map will show you which states belong in that zone. And, your seed packet will tell you which zone that plant will survive in.

Similarly, you can look up the plants that are best suited for your zone online.

That said, it doesn’t mean that you can’t grow plants that aren’t in your zone, because you can. But, it will be harder. And, you need to take extra care and do some added maintenance to help them flourish.

In most cases, you’ll need to bring them indoors when the temperature drops during wintertime. Then, take them back outside when spring arrives.

Important Note: If you live on the West Coast, you’ll be better served by looking at the Sunset Climate Zones. While you can check the USDA Plant Hardiness Zone Map, I’ve found the different terrain of the western states and varying weather conditions makes the Sunset Climate Zones a better choice.

 

What Planting Zone Do I Live In? (How to Find Out Your Planting Zone)

So how do you find your hardiness zone?

Actually, it’s simple. All you need to do it go to the USDA Plant Hardiness Zone Map page. This will show you an interactive map that you can use to get more information about what your zone is and what kind of temperatures it gets.

Step 1: Click on your state. Similarly, you can go to the top drop-down list and choose your state. Doing so will show you a “zoomed in” version of your state instead of the entire U.S.

Step 2. From there, you’ll be able to pinpoint your location and see the climate it receives. That way, you’ll know which plants are best suited for your region as well as what zone you’re in.

Step 3. A quicker way to get your specific zone is to enter your ZIP code on the upper left-hand box. This will give you your Zone number as well as the temperature range.

 

Related

 

How to Use Your Planting Zone

If you remember the section above on annuals and perennials, you’ll know that some plants (annuals) aren’t meant to last the winter.

As such, if you’re planting annuals, you don’t need the USDA Plant Hardiness Zone Map. After all, annuals will die as wintertime begins. So, there’s no need to go through the trouble.

But, if you’re planting perennials or other woody plants like shrubs (which survive for years), then it’s important to consider the planting zones. That’s because you want these plants to survive the winters.

Plants experiencing winters beyond their recommended zones often get damaged by the extreme cold and frost. As such, avoiding this helps prevent any issues later on.

The plant zone map helps you figure out which plants are hardy for the kind of temperatures your location receives at its coldest point.

As for annuals, you’re better off looking at how long the growing season is, when the best time to plant is and when the first and last frost dates happen in your area.

Since they’re meant to last for one season only, you want to know when’s the best time to start to get the most out of them. And, when you should expect them to start slowing down. That way you don’t end up planting just before the frost comes.

 

Can You Grow Plants Outside Your Zone?

Yes. But, it depends.

For example, if you live in USDA Zone 6, this means:

  • You ought to be able to grow plants that are hardy to Zone 6.
  • You can also grow plants that are labeled for zones that are colder. Basically, if the plants can survive temperatures colder than yours, they should be okay with your location. I hope that makes sense. And since the lower zones are colder, you should be able to grow plants that are below your zone. So, in this case that includes plants hardy to zones 3, 4 & 5.
  • You likely won’t be able to grow plants that are meant for zones higher than yours. That’s because they aren’t fit for climates lower than their zone, which yours is. So, you’ll have a hard time growing plants in labeled for zones 7 & 8 unless you take extra measures to keep them safe and warmer during the winters. Then, you may have a chance. Otherwise doing so may damage or kill them.

The only exception to this is if you “bypass” the winter altogether. You can do so by bringing the plants indoors when temperatures drop outside. This way, they remain toasty through the cold months.

Note: Most plants aren’t limited to one USDA Plant Hardiness Zone. For example, sunflowers are hardy to USDA Zones 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. This means as long as your zone is on the list, it should do well for you.