The United States Department of Agriculture (USDA) Plant Hardiness Zone (PHZ) Map is the standard resource for determining which perennial plants can survive the winter in a specific location. This map divides the country into zones based on the lowest average winter temperatures, providing a framework for successful long-term gardening. Understanding your local hardiness zone indicates the minimum cold tolerance a plant must possess to overwinter successfully.
Albuquerque’s USDA Plant Hardiness Zone
Albuquerque, New Mexico, primarily falls across two subzones: USDA Plant Hardiness Zones 7a and 7b, according to the 2023 map update. Zone 7a, covering the western and higher-elevation edges of the city, is defined by an average annual minimum winter temperature range of 0°F to 5°F. The most common designation for the majority of the metropolitan area is Zone 7b, representing a slightly warmer range of 5°F to 10°F. Some lower-elevation, sheltered areas have even been upgraded to Zone 8a, which indicates a minimum temperature range of 10°F to 15°F.
How Hardiness Zones are Calculated
The USDA establishes hardiness zones based exclusively on the average annual extreme minimum winter temperature for a given location. This metric is calculated by averaging the absolute coldest temperature recorded each year over a 30-year period, with the 2023 map utilizing data from 1991 to 2020. This long-term average predicts the lowest temperature a plant is likely to experience.
The system divides the North American continent into zones separated by 10-degree Fahrenheit increments. Each full zone is further subdivided into ‘a’ and ‘b’ subzones to provide more precise guidance. These subzones are separated by a 5-degree Fahrenheit difference, with the ‘a’ subzone being the colder half and the ‘b’ subzone being the warmer half.
Accounting for Local Microclimates
Despite the precision of the USDA map, the broad zone designation does not account for localized environmental factors known as microclimates, which can significantly alter the temperature on a property. Albuquerque’s varied geography, including its proximity to the Sandia Mountains and the Rio Grande Valley, creates substantial microclimatic differences within the city limits.
Areas at higher elevations near the Sandia foothills often experience colder winter lows and stronger winds, creating conditions that feel more like Zone 6. Conversely, the urban heat island effect in the densely built valley and downtown areas tends to retain heat, resulting in warmer nighttime temperatures that mimic a higher zone. Gardeners can use these effects to their advantage, such as planting heat-loving species against a south-facing masonry wall, which absorbs and radiates heat. Similarly, low-lying parts of a yard can become “frost pockets” where cold air settles, requiring plants with greater cold tolerance.