What is the USDA’s Plant Hardiness Zone Map?

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Gardeners must consider several factors before deciding which plants they want to plant. Perhaps the most crucial of these factors is the area’s climate and if it is one in which the plant can thrive!

The US Department of Agriculture (USDA) Plant Hardiness Zone Map can help determine which plants are best for each climate.

USDA hardiness zone maps

The USDA Plant Hardiness Zone Map details plant hardiness zones across the country. The USDA published the first map of USDA planting zones in 1960 under the American Horticultural Society’s sponsorship and the US National Arboretum.

These zones, often called growing zones or planting zones, allow gardeners to make informed decisions regarding which plants to grow per their climate.

How Is the USDA Plant Hardiness Zone Map Used?

Here’s a classic USDA hardiness map. It cites the average annual minimum temperature from 1967 – 2005 in Fahrenheit and Celsius. (Map Credit: USDA Gov, Agricultural Research Service, Mapping by PRISM Climate Group at Oregon State University.)

Gardeners can consult their USDA zone state maps and choose which plants to grow based on the suggested plants’ list.

Click here for printable copies of the USDA Plant Hardiness Zone Map!

Many nurseries offer their own version of the plant zone map. These maps make it easy to filter for plants that will grow well in your zone.

The USDA Plant Hardiness Zone Map was created based on each zone’s average annual extreme minimum temperatures, which means it doesn’t account for specific temperatures.

The average annual extreme minimum temperatures refer to how cold each zone location can get each year. Plant hardiness has to do with their likelihood of surviving the extreme cold of that zone.

For instance, plants described as being “hardy to zone 5” can survive the lowest annual temperature in that zone, which is –20 degrees F.

Gardeners should keep in mind that the map does not consider average maximum temperatures. The microclimates of their gardens may be of zones higher and lower than indicated on the map.

The USDA Plant Hardiness Zone Map exists to guide gardeners and plant growers, but it’s entirely possible for plants meant to grow in one zone to end up growing in another based on microclimate.

Did you know?

Are you frustrated trying to find the correct USDA zone in a hurry? I use this handy USDA plant hardiness zone interactive map when I need accurate zoning data. Finding your location’s plant hardiness zone information is straightforward – and fast.

Here’s how it works – click on your state (or type your zip code), and you’ll discover your correct USDA zone plus the average annual temperature and temperature range history. Without the guesswork. Nice!

Understanding Microclimates

Beginners may want to stick with plants that can be grown in their zones, but more experienced gardeners usually plant according to microclimates.

Microclimates are parts of the property that may have a different climate than those indicated for their area or macroclimate in the zone map.

For example, they might notice that a part of their backyard is warmer than the rest or hidden from frost, creating an excellent place to experiment with plants.

Planting based on microclimates doesn’t always work out, but it is worth trying.

However, temperatures aren’t the only thing gardeners have to consider when farming based on microclimates. They also need to look at whether the plant enjoys full sun or partial shade, or even dry or wet soil.

Gardeners that don’t naturally have a microclimate can create one by creating unique structures or planting spaces. Walls can provide shelter and heat for plants, just like hedges or storage sheds.

Read More – What to Do With Tomato Plants During Winter?

Understanding Hardiness Zones

The USDA Plant Hardiness Zone Map available on the USDA website is the 2012 version developed by the USDA Agricultural Research Service with help from Oregon State University’s PRISM Climate Group.

The map is occasionally updated, but the changes are generally of significance only to professionals.

The plan is formulated based on the average annual extreme minimum temperature, or average annual minimum winter temperature, during the previous 30 years. These temperatures are then divided into 10-degree F zones.

The map details 13 zones across the US and Canada, with each zone having a winter temperature 10 degrees warmer or colder than the next.

The zones are listed from the most northern to the most southern; sections of Alaska make up zone 1, while parts of northern Minnesota are in zones 2 and 3.

Most of America can be found in zones 4 to 8, while central and southern Florida make up zones 9 to 11. Hawaii and Puerto Rico are in zones 12 and 13. Some zones never get snow, while others always do.

When purchasing plants and seeds, check the packaging for the suggested hardiness zones.

Gardeners need not worry if their hardiness zone changes in updated editions of the hardiness zone map because the plants may still thrive, regardless of the map’s suggestions.

The map acts only as a guide. Past weather is not a reliable predictor of future climate.

Other Hardiness Maps

Here’s a vintage hardiness map from May 1st, 1967. It was made by The Arnold Arboretum at Harvard University in Massachusetts. (Map Credit: USDA Gov, The Arnold Arboretum.)

The USDA Plant Hardiness Zone Map is not the only hardiness zone map in the world.

The UK and Australia have their own maps but do not update them as frequently as those used in the US. Some gardeners do consult them, however, to gather information on possible plants to grow at home.

(Gardening buffs may wish to read the plant hardiness zones for Australia published within the Australian National Botanic Gardens archive. However, the map is from 1991.)

The “Sunset climate zones” system is also gaining traction in the west. While the USDA’s map, predominantly used in the east, considers average annual minimum temperature, the Sunset climate zones consider several factors.

These include winter lows, summer highs, wind, humidity, how much rainfall the zone receives and when, and how long each zone’s growing season is.

Plant growers who follow the USDA Plant Hardiness Zone Map are advised to consider similar environmental factors when gardening, aside from the temperatures indicated by their hardiness zone.

Plants that need full sun may lack light when placed in an area with partial shade, just like they may suffer moisture stress if their soil isn’t as moist as it should be.

Some plants have no problem with exposure to the cold but may risk injury if their climate stays chilled for an extended period.

Low humidity may also lead to plant damage during the cold. Other factors, such as snow, pollution, size, and landscape, should not be overlooked.

Did you know?

Another excellent gardening tool for American homesteaders is the first frost date calculator from Farmer’s Almanac. The calculator uses information from NCEI – the National Centers for Environmental Information.

The first frost date calculator on Old Farmer’s Almanac doesn’t offer as much data as the USDA Plant Hardiness Zone Map.

And, unfortunately, the calculator only works for the US and Canada. But, it’s still a fast resource if you’re unsure of when to start your zucchini and tomato plants!

The USDA Plant Hardiness Map – Should You Use It?

Yes! The USDA Hardiness map is a great way to figure out which crops to grow in your region. But – while the USDA Plant Hardiness Zone Map helps gardeners know which plants to grow and which of their plants may survive over time, experts warn not to view it strictly. 

According to the National Gardening Association, differences in climate in the west are not adequately addressed on the map. One area may always be dry and another wet, but still, be in the same zone.

Knowledge of one’s hardiness zone is helpful, but gardeners still have the final say in their own backyard!

What hardiness zone are you homesteading and gardening from? Please reply and let us know!

Read More – Here’s How to Build a Core Garden That Feeds Itself!

Works Cited:

Credit for Blog Featured Image:

“20120106-OC-AMW-0094” by USDAgov is marked under CC PDM 1.0. To view the terms, visit https://creativecommons.org/publicdomain/mark/1.0

Credit for USDA Hardiness Maps:

“20120106-OC-AMW-0098” by USDAgov is marked under CC PDM 1.0. To view the terms, visit https://creativecommons.org/publicdomain/mark/1.0

“20120106-OC-AMW-0096” by USDAgov is marked under CC PDM 1.0. To view the terms, visit https://creativecommons.org/publicdomain/mark/1.0

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