Hardiness Zones Explained: What the Numbers Mean and How to Find Your Growing Zone

The term "Hardiness Zone" is something you often hear in plant nurseries and gardening circles. Each plant is marked with a number that corresponds to a certain zone; this allows people to figure out which plants will grow in what areas. But what exactly do these numbers mean, and are they really that important?

Also called planting zones or growing zones, hardiness zones are one of the most important factors to consider when deciding whether to buy a plant or not. Hardiness zones are a metric used to determine whether or not a certain plant will overwinter in a particular area, based on average minimum winter temperatures.

Keep reading for a more detailed explanation of hardiness zones; why they work and what factors they don’t account for, as well as how to find your hardiness zone.  

What are hardiness zones?

Plants thrive in different climates—we all know that to be true. Some plants are better-suited to colder temperatures than others, and many plants are more tolerant of heat and drought than their counterparts. < Also called planting zones or growing zones, hardiness zones are an attempt by botanists and gardeners to categorize plants by their ability to thrive in a given area based on average minimum winter temperatures. It’s not a perfect system, because more factors than just temperature contribute to an area’s climate. Humidity, rainfall, day length, and soil type are equally important factors that affect whether or not certain plants will thrive or struggle in any given area. However, hardiness zones are the most widely recognized system for growers to communicate with one another about which plants will survive in which regions. 

How to find your hardiness zone by zip code

Head over to our FAQ page and browse our Hardiness Zone Map for a general idea of what zone you live and garden in.  For a more detailed map, go to the United States Department of Agriculture’s Plant Hardiness Zone Map and type your zip code or nearest city into the search box, and the map will pinpoint your exact location. 

The USDA Hardiness Zone Map

The creation of today’s hardiness zones is attributed to a German-American gardener and scientist, Alfred Rehder—according to Harvard University’s Arnold Arboretum archives. The original hardiness zone map was created in 1927 and includes eight zones. Today’s map, which divides the United States into 13 different zones, was adopted in 1990.  The 13 zones are numbered 1 to 13, with 1 being the coldest and 13 being the warmest. You’ll notice that the major hardiness zones are divided by degrees of 10, and each zone is further subdivided by five degrees; these are marked a and b. So for example, Zone 7 includes all regions whose average minimum temperature falls between 0℉ and 10℉. Zone 7a represents the colder end of that range, 0℉ to 5℉, and Zone 7b represents the warmer spectrum, from 5℉ to 10℉. 

AHS Heat Zone Map

Since cold temperatures and hardiness zones aren’t the only metrics used to measure how well a plant will thrive in a particular area, the American Horticultural Society developed another map, the Heat Zone Map. This map breaks down the country into 12 regions characterized by how many days of the year are over 86℉ in that region. Though not nearly as popular as USDA Hardiness Zones, heat zones are another metric you can use to determine if certain plants will thrive in your area. 

Sunset Climate Zones

Growers on the west coast have yet another option to estimate if a plant will grow well in their area, called Climate Zones. Born out of a collaboration between the University of California and Sunset Magazine, climate zones break down the western portion of the United States into 15 distinct regions with unique climates defined by elevation, average rainfall, humidity, and the number of frost-free days. 

Understanding hardiness zones at GoBuyPlants

All of our plants at the GoBuyPlants nursery thrive in a range of temperatures and hardiness zones. Our plants will be marked with at least two numbers, and often more. For example, Island Bonfire Daylily is designated for hardiness zones 4–9. This means that this particular plant will overwinter in hardiness zones 4, 5, 6, 7, 8, and 9—that’s six hardiness zones! 

Tips for shopping our online nursery worry-free

Hardiness zone is a good indicator of how well a plant will do in your area, but it isn’t the only indicator. We recommend that folks only purchase plants that suit their hardiness zone, but experienced gardeners may have a little room for experimentation.

  1. Know your hardiness zone. 

  2. First and foremost, look for plants that are recommended for your hardiness zone. These plants are already adapted to your area, and are more likely to thrive in your region with less work.

  3. Pay close attention to plant care instructions. 

  4. If a plant is recommended for your hardiness zone, it will very likely do well—with the proper care. Make sure you understand what soil type and pH the plant prefers, and note how much sunlight and water it needs. 

  5. Consider any microclimates in your garden. 

  6. A microclimate is a small area within your garden that has different environmental conditions than the surrounding areas. For example, a south-facing wall may be warmer and sunnier than other areas of your garden, creating a microclimate that could potentially suit some plants that are technically outside of your hardiness zone.

  7. Protect plants from extreme weather.

  8. Within any given hardiness zone, temperatures may fluctuate from year to year, so keep an eye on the weather, especially during the more volatile seasons of spring and fall. Take steps to protect your plants from drastic weather changes, such as unexpected freezes or heat waves. This may involve covering your plants with tarps or blankets on a cold night or providing shade during hot weather.

    Experiment with different types of plants to see what works best in your particular zone and microclimate. If you’re drawn to a plant that isn’t a good fit for your hardiness zone, you might still be able to grow it. You can always bring your cold-sensitive plants inside for the winter and you can create a cooler microclimate for your heat-sensitive plants.

    Gardening is all about trial and error, so don't be afraid to try new things and learn from your successes and failures. By following these tips and paying close attention to the hardiness zones, you can create a beautiful and thriving garden that is well-suited to your particular environment.


At the end of the day, hardiness zones exist so that growers can have a pretty good guess of which plants will thrive in their gardens and which plants won’t. Now that you know your hardiness zone, shop our extensive selection of perennials and shrubs to find the perfect fit for your garden.