Arizona Growing Zones Explained

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Sarah Caldwell

Sarah Caldwell has five years of writing experience that she uses to pursue her passion for gardening. When she isn’t spending time with her family, she’s writing about the best kept secrets and tips to grow a beautiful garden! She knows how frustrating it can be to try to grow a flourishing garden without any gardening experience. She’s here to share with you the tips you need to know to skip over mistakes that’ll hold you back from getting the garden of your dreams.

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Plants grow best in the climates to which they are best adapted. Arizona is a place that most people think of as a desert, but Arizona has some of the most drastic climate changes of any other state, and there are a wide variety of plants that grow well in all areas of the state.

One of the factors that will make you most successful in growing your own plants is knowing the climate zone in your location. Soil, water, and light are also critical, but the temperature is a severely limiting factor.

Arizona spans 335 miles from east to west and 390 miles from north to south. The diversity of climate zones is influenced by elevation and rainfall. While there are only about 3 inches of rainfall per year in cities like Yuma and Phoenix, there can be more than 30 inches in the mountains of Show Low or Pine.

Most of Arizona’s climate is considered arid or semi-arid due to a great deal of evapotranspiration, which is the loss of water from plants and soil. Evapotranspiration happens at a higher rate than the amount of rainfall most zones in Arizona receive.

About Climate Zones

It’s important to understand the limitations of growing in certain locations because it helps you select the plants that have the greatest chance for long-term success. If there’s an early freeze in the fall before plants have hardened or a late freeze in the spring after plants have started to flower, it can cause a lot of damage, even if the minimum annual temperatures aren’t exceeded.

For plants to thrive in a particular location, factors like temperature, planting timeframes, wind, light, water availability, soil quality, and exposure to these extreme weather conditions must all be considered for plant health and growth.

Climate zone classifications give a good indication of rainfall patterns and long-term temperatures that can affect natural vegetation. While irrigation is available in areas that lack rainfall and soil conditions can be manipulated, minimum and maximum temperatures cannot be changed.

There are three climate zone maps that use different criteria to help gardeners choose the correct plants for each zone.

USDA Hardiness Zone Map

This map classifies climate zones by the average annual minimum temperature in winter. It uses temperatures collected from 1976-2005. Zones are labeled from 1 to 13 in 10-degree increments, but also contain subzones labeled a and b according to 5-degree fluctuations.

Zone 1 starts at -60 degrees Fahrenheit while Zone 13 refers to climates that don’t drop below 50 degrees. Arizona’s zones range from 4b to 10b. The coldest locations, like the White Mountains, Mount Graham, and the San Francisco Peaks drop as low as -20 degrees.

Flagstaff resides in Zone 6a and can get as cold as -10 degrees. Plants in these zones must be hardy enough to survive these cold temperatures.

The warmest Arizona climates are in the south-central and southwest parts of the state. That includes the Phoenix metropolitan area and everything along the Colorado River, where temperatures rarely drop below 30 degrees and only drop this low at night in the wintertime.

This map is extremely accurate for Arizona residents and is useful when selecting appropriate plant materials for a specific location. Even microclimates are affected by immediate surrounding areas. These microclimates are often warmer in urban areas where heat is stored, absorbed, or reflected. Microclimates are colder along rivers and washes where temperature inversions are more likely to occur.

When choosing plants, you can look at the USDA hardiness zone they’re appropriate for. Every plant is evaluated based on trials conducted by nurseries, botanical gardens, and research organizations.

The ratings on these plants indicate their long-term survival in the coldest climate where they were successful. You can find these ratings in nursery catalogs, horticulture books, and websites. It’s also common to see slight variations in these ratings based on different species of the plants or different testing entities.

It’s important to remember that cold is only one variable that plants experience throughout the year. In fact, USDA zones 9a and 9b are common in southern Arizona, but also occur on the tip of the Olympic Peninsula in Washington and along the Oregon coast. While the average minimum temperature in these zones is the same, Arizona experiences more drastic daily fluctuations as well as extremely high summer temperatures and very low humidity.

Plants chosen for zones 9a and 9b in Arizona must be more hardy and able to tolerate the stress that comes from high summer temperatures whereas plants in zones 9a and 9b in Washington and Oregon may be less hardy.

Sunset Climate Zones

This map of zones is a better determiner of plants that will be successful in the Southwest because it’s a comprehensive source for choosing plant material that’s well adapted to desert climates.

The Sunset climate zones take into account things like high and low temperatures, elevation, latitude, humidity, first and last frost dates, growing season, amount and annual pattern of rainfall, and ocean and continental air influence.

Arizona’s warmest climates are in Sunset climate zone 13. These are the subtropical desert areas that may reach elevations of 1100 feet. It includes Yuma, Phoenix, and locations along the Colorado River. Average summer temperatures can reach 107 degrees, but because there are as many as 15 freezing nights in the winter, it limits the plants that can be planted here. Some tender subtropical plants may be successful if planted in protected areas.

Zone 12 includes the intermediate desert with summer temperatures about 5 degrees cooler than zone 13 on average. Deciduous fruit trees are successful here as long as they have a low chilling requirement of fewer than 300 hours at between 32 and 45 degrees. Plants in this zone should be tolerant of cold.

The high desert areas of Arizona are in Sunset climate zone 10 and have elevations of 3300-5000 feet. There are 75-100 nights of freezing temperatures in this zone and -10 degrees have been recorded. The growing season is from April to November.

Mountain and intermountain climates like Flagstaff and Prescott reside in zone 3A. This is the shortest growing season, from May to October. Average winter temperatures range from 15-25 degrees. There’s a small area in the southeastern and the northern part of the state that is in zone 3B. It’s similar to zone 3A with warmer seasons and a slightly longer growing season.

Southeastern Arizona and the Colorado Plateau are in zone 2B. They have a relatively warm growing season from May to September and average winter temperatures are 12-22 degrees.

Zones 2A and 1A are the coldest zones in the state and are at the highest elevations. They have long, snowy winters and very short growing seasons. The plant palette is restricted to herbaceous perennials, some deciduous woody plants, and hardy evergreens.

Plant Heat Zone Map

This map was developed by the American Horticultural Society (AHS) in 1997. It uses daily highs recorded by the National Weather Service from 1974-1995. There are 12 zones classified by the number of days with temperatures over 86 degrees Fahrenheit.

This map assumes that plants will start experiencing heat stress and cell damage at or above this temperature, but sometimes this is incorrect. While zone 1 has less than one heat day a year, zone 12 has more than 210. Arizona’s heat zones range from 4-11. Zone 4 has 15-30 heat days at higher elevations in the north while zone 11 has 180-210 heat days. The Colorado Plateau and the Transition zone are in zones 4-8 with 14-120 heat days.

These heat zones are relevant for plants that suffer from heat stress, but most plants native to or adapted to the Arizona desert actually thrive at temperatures well over 86 degrees, even when it’s that hot on a daily basis.

Arizona Climate Zones

There are three physiographic landforms that influence Arizona’s climate the most. However, within each of these zones are diverse geographical components that create microclimates in pockets that can cause the weather to change drastically within a short distance.

Here’s some more detail on how each zone affects Arizona’s climate.

The Colorado Plateau

This plateau varies in elevation from 5000-8000 feet and is in the northern part of the state. There’s only a narrow strip along the northwest border of the state that isn’t a part of this landform.

The Colorado Plateau ends with the Mogollon Rim at the south, which is a steep slope that drops 2000-3000 feet.

The Transition Zone

This zone is also called the Central Highlands and is filled with rugged mountains. It’s nestled in between the Colorado Plateau and the Basin and Range.

Basin and Range

This zone is at the southern part of the state, along the Colorado River and slightly to the north. It’s characterized by lowland desert, but does have some mountain ranges. This is a year-round warm climate at low elevations.

Arizona Cities and Classifications

Tree Zones

Accent Plant and Shrub Zones

FAQs

Final Thoughts

When determining what to plant in your garden in Arizona, you need to evaluate your zone. Arizona climates range widely and span nearly every zone on all three zone maps. Look for your area on each map to determine which plants will grow the best.

Recommended Reads:

• Oklahoma Planting Zone Guide