Arizona Plant Climate Zones
by Cathy Rymer, Certified Arborist
(Climate zone information courtesy of Sunset Magazine)
The climate zones of Arizona are as varied as our region, ranging from sub-alpine to tropical desert. Before planting trees in our state it's important to know how local climate affects plant growth. In addition to the minimum temperatures that trees can withstand, be sure to make note of varying conditions in your area such as reflected heat or high humidity. These are referred to as micro climates that take into consideration factors like sun exposures, wind or airflow, humidity, soil, paved areas, shade, structures and even hills and valleys.
The climate zones listed below are those used by Sunset. Sunset's climate zones consider temperature as well as other important factors including the total climate, length of growing season, timing and amount of rainfall, winter lows, summer highs, wind, and humidity. This is unlike the USDA, which divides most of North America into zones based strictly on winter lows.
The discussion of each climate zone lists several appropriate trees. Climates of adjoining zones blend into each other near their boundaries, making it possible to grow some plants from each region. There will be many to choose from and we encourage you to investigate the choices. Geographical sites, cities and towns are included as a reference for each zone.
Coldest mountain and intermountain areas of the contiguous states
Marked by a short growing season and relatively mild summer temperatures, Zone 1A includes the coldest regions west of the Rockies and is characterized by mild days and chilly nights during the growing season. Reliable snow cover insulates plants in winter. In years when snow comes late or leaves early, protect plants with a 5- or 6-inch layer of organic mulch. Along with hardy evergreen conifers, tough deciduous trees and shrubs form the landscape's backbone. Winter lows average in the 0 to 11°F range; extremes range from –25 to –50°F.
Quaking Aspen, Douglas fir, and Engelmann Spruce can be found here.
Point of reference sites include Greer, Alpine and Hannagan Meadow.
Click here for the Zone 1A Planting Guide
Cold mountain and intermountain areas
Another snowy winter climate, Zone 2A covers several regions considered mild compared with surrounding climates. You'll find this zone in the sky island mountain areas of southeast Arizona. Winter temperatures here usually hover between 10 and 20°F at night, with drops between –20 and –30°F every few years. The growing season is 100 to 150 days.
White Fir, Alligator Juniper, Colorado Blue Spruce and Gambel Oak.
Reference areas include the highest elevations of the Catalina, Rincon and Pinaleño mountains.
Click here for the Zones 2A and 2B Planting Guide
Warmer-summer intermountain climate
This is a zone that offers a good balance of long, warm summers and chilly winters. This zone stretches over large areas of northern Arizona. Zone 2B is home to the largest contiguous stand of Ponderosa Pine trees in the world! Winter temperatures are milder than in neighboring Zone 2A, minimums averaging from 12 to 22°F, with extremes in the –10 to –20°F range. The growing season runs from 115 days in higher elevations to more than 160 days at lower elevations.
Trees such as Silver Maple, Arizona Sycamore, Boxelder, Flowering Pear and Ponderosa Pine are common.
Reference towns include Flagstaff, Window Rock, Williams and Fredonia.
Click here for the Zones 2A and 2B Planting Guide
Mild areas of mountain and intermountain climates
You can hardly find a better landscaping climate than Zone 3A. This zone tends to occur at higher elevations in Arizona where winter minimum temperatures average from 15 to 25°F, with extremes between –8 and –18°F. Its frost-free growing season runs from 150 to 186 days. This is another great zone for all kinds of deciduous fruit and ornamental trees. Supplemental irrigation may be needed during dry spells.
Pinyon Pine, Red Oak, Black Locust, Austrian Pine
Point of reference towns include Prescott, Payson, Winslow, Holbrook, St. Johns
Click here for the Zons 3A and 3B Planting Guide
Mildest areas of intermountain climates
Zone 3B is much like Zone 3A, but with slightly milder winter averages of 19 to 29°F and extremes that usually bottom out between –2 and –15°F. Summer temperatures are a bit higher than in Zone 3A — mostly in the high 80s and low- to mid-90s. Zone 3B offers one of the longest growing seasons of the intermountain climates with 180 to 210 frost-free days with plenty of heat. However, it's one of the smallest zones.
Good tree choices are Atlas Cedar, Thornless Honey Locust, Chinese Pistache, Desert Willow
Reference towns: Prescott Valley, Tuba City, Morenci
Click here for the Zones 3A and 3B Planting Guide
High desert areas of Arizona
This zone consists mostly of the 3,300- to 5,000-foot elevations in Arizona. Zone 10 has a definite winter season — 75 to more than 100 nights below 32°F. That favors deciduous fruits, though late frosts can work against apricot crops. Average winter minimums range from 32 to 23°F (0 to –5°C). Lows of 25 to 22°F often come in. The cold winter season calls for spring planting. Growing seasons are very long — up to 225 days.
Try trees such as Chinese Pistache, Netleaf Hackberry Evergreen Elm or Arizona Cypress.
Point of reference towns include Camp Verde, Kingman, Benson, Globe, Sedona, Bisbee, Nogales
Click here for the Zone 10 Planting Guide
Arizona's intermediate desert
The crucial difference between Arizona's intermediate desert (Zone 12) and the low desert (Zone 13) is winter cold. But though the intermediate desert averages only five more freezing nights than the low desert (20 in Tucson compared with 15 in Phoenix), it has harder frosts spread over a longer cold season. Zone 12 averages about eight months between freezes, nine months between killing frosts of 28°F or lower. Zone 13, on the other hand, averages more than 11 months between killing frosts, when it gets them at all. Extreme low temperatures of 6°F have been recorded in Zone 12.
The mean maximums in July and August are 5 or 6°F cooler than the highs of Zone 13. Many subtropicals that do well in Zone 13 aren't reliably hardy here, but succeed with protection against the extreme winters. Although winter temperatures are lower than in Zone 13, the total hours of cold are not enough to provide sufficient winter chilling for some deciduous fruits. From March to May, strong winds (to 40 miles per hour) can damage young tender growth. Windbreaks help. Here, as in Zone 13 and the eastern parts of Zone 10, summer rains are to be expected and can be more dependable than winter rains.
Trees like Mesquite (all species), Afghan Pine, Chitalpa and many Acacia species do well here.
Reference towns include Tucson, Wickenburg, Safford, and Florence
Click here for the Zone 12 Planting Guide
Low or subtropical desert areas
Ranging from just above sea level in Yuma to 1,100 feet around Phoenix, Zone 13 is a subtropical desert. Average summer high is 107°F. Winters are short and mild, with brief frosts occurring up to 15 nights per year.
Average winter minimums range from 36 to 42°F, with extreme lows from 27 to 15°F. The planting season begins in fall. Spring winds can set back plants, but summer storms cool down landscapes and supply a little extra water. Supplemental irrigation is a must for most trees.
Heat loving trees like Palo Verde, Ironwood, Desert Willow and Sissoo are good choices.
Reference towns include Phoenix, Yuma, Casa Grande, and Parker
Click here for the Zone 13 Planting Guide