Arizona is a state of immense geographic and climatic contrasts, making the question of “What zone is it in?” dependent entirely on the context. From scorching low deserts to alpine mountain peaks, the state’s diversity means it falls into multiple distinct categories for time, agriculture, and general climate classification. The time zone involves a unique exception, while the planting and climate zones reveal a vast temperature gradient across the landscape. Local conditions vary dramatically from one region to the next.
Time Zone Status and DST Exception
Most of Arizona operates under Mountain Standard Time (MST) throughout the entire year, maintaining a consistent offset of UTC-7. The state opted out of observing Daylight Saving Time (DST) in 1968, a choice driven by its extreme summer heat.
This year-round adherence to MST creates a seasonal shift relative to neighboring states. From November to March, Arizona shares the same time with Mountain Time states. When those states spring forward to Mountain Daylight Time (MDT), they become one hour ahead.
During the summer, Arizona’s time aligns with states observing Pacific Daylight Time (PDT), such as California and Nevada. The state effectively switches its time relationship twice a year without changing its own clocks. This consistent time-keeping allows the sun to set an hour earlier during the hottest months, enabling residents to enjoy cooler outdoor activities sooner.
The Navajo Nation Exception
The one exception to Arizona’s no-DST rule is the Navajo Nation, a large territory spanning parts of Arizona, New Mexico, and Utah. To maintain a single time standard across its land, the Navajo Nation observes Daylight Saving Time concurrently with the rest of the United States.
Visitors traveling through northeastern Arizona must adjust their clocks by an hour when crossing the boundary during the DST period. The Hopi Reservation, which is surrounded by the Navajo Nation, adheres to the state’s general MST rule, creating a time-keeping island within the territory that observes DST.
Hardiness Zones for Planting
Arizona is classified using the USDA Plant Hardiness Zone Map, based on the average annual minimum winter temperature. This system determines which perennial plants can survive the winter cold. Zones are extremely diverse, ranging from the cold 4b/5a in the highest elevations to the warm 10b/11a in the low deserts.
The coldest zones, such as 4b, are found in mountainous regions like the San Francisco Peaks, where minimum temperatures can drop below -20°F. Low-lying areas like the Phoenix metropolitan area fall into Zone 10a or 10b (30°F to 40°F minimum). This milder winter allows a broader range of subtropical plants to survive outdoors.
Flagstaff sits in a much colder zone, typically 6a, indicating that plants must tolerate winter lows between -10°F and -5°F. The dramatic shift in zones over short distances highlights the profound influence of elevation on local climate.
Defining Arizona’s Climate Zones
Arizona’s climate is broadly categorized into three major regions: the Low Desert, the High Desert/Plateau, and the Mountain regions.
Low Desert
The Low Desert, including the Sonoran and Mojave Deserts, is characterized by extremely hot summers (frequently exceeding 100°F) and mild winters with occasional light frost. This region receives minimal annual rainfall and is subject to intense solar radiation.
High Desert/Plateau
Moving north and into higher elevations is the High Desert and Plateau region, encompassing areas like the Colorado Plateau. This transitional zone experiences greater temperature swings, with hot summers that are less extreme than the low desert and noticeably cooler winters. The High Desert typically sees four distinct seasons and slightly more precipitation, often as winter snow.
Mountain Regions
The Mountain regions, particularly along the Mogollon Rim and the state’s highest peaks, have the most temperate climate overall. These areas feature cold, snowy winters and mild to cool summers, with the highest annual precipitation totals. The significant elevation gain fosters dense forests of ponderosa pine and mixed conifers, contrasting sharply with the lower elevations.