What Are Plant Hardiness Zones and How do they Work?

Kate Mitchell

May 24, 2023

What are hardiness zones?

Plant hardiness zones are areas determined by temperature that help gardeners to choose plants that can thrive in the region they live in. In the USA we tend to go by the USDA plant hardiness zone map, and the 2012 version is the current standard.

On this map, the color-coded zones are determined by the average minimum winter temperature. For any given zone, we can predict what the lowest temperature is likely to be each winter. This gives gardeners a good idea of which plants will be able to survive the coldest temperatures in their area.

Red and green leaves coated in frost

Zone 1 is the coldest zone, with winter temperatures regularly dropping to -50 to -60 degrees Fahrenheit. The northern parts of Alaska are in Zone 1. In Zone 2, the winter lows are generally ten degrees warmer (-40 to -50 degrees F). Zone 2 covers parts of Alaska and some areas of Wyoming.

As the zone numbers increase, the average minimum temperature goes up. South Florida comes into Zone 10, most of Hawaii is in Zone 11 and Puerto Rico is covered by Zones 12 and 13.

Temperatures vary locally, so it's not a case of straight bands across the country. North or South, most states include at least three zones. You can use the zip code search to find your city or region.

Are hardiness zones fully reliable?

Hardiness zones are based on the lowest average annual temperature in different regions across North America. Although they give a general idea of which plants are likely to thrive where you live, there is other information that you need to consider as well.

Green stems covered in frost

It's not only the coldest temperature your region will encounter over the winter that's important. It also makes a difference how many days (or nights) your plants will be exposed to those conditions. Some areas could only hit that cold spot once or twice over the winter, whilst in others it might be constant for a few months. This could be too much for some plants. On the other hand, some plants require a certain number of cold days during the winter so they can bear fruit.

Other factors that can affect your plants' ability to thrive include soil type, humidity and wind chill. Hardiness zones also don't account for high temperatures, only the lows. Plants that cannot cope with tropical conditions or hot, dry weather may struggle even if they are hardy in your zone.

Choosing plants for your Zone

Planting zones are useful because, with their estimate of the lowest winter temperatures in each different region, they give a good idea of whether a particular plant species is likely to survive the cold period each year. Before you buy a perennial plant you can check the hardiness zone to see if the climatic conditions where you live are likely to let it survive until the next growing season.

A man examines plants for sale

If you're set on having a particular plant that is not hardy in the zone where you live, there may still be a way you can enjoy the fragrant flowers or attractive foliage you want. One great option is to use a container, which you can bring indoors if frost or cold temperatures are forecast. Rushfields has some more information here on how to protect non-hardy plants from cold winter temperatures.

A good way to be sure that your beds will stay healthy is to choose native plants. If a plant grows happily in the wild, the chances are that it will also thrive in your yard or garden. UF Gardening Solutions has a helpful list of native Florida plants that will work well in your landscape.

But the easiest way to ensure that your landscape will continue to thrive in beauty and harmony is to consult a professional landscaping service such as LawnMore. Our experts can help you choose the right plants and maintain your outdoor space so you can take lasting joy in your landscape for years to come.

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