The United States Department of Agriculture (USDA) Plant Hardiness Zone Map is the standard tool gardeners use to determine which perennial plants can reliably survive the winter. This system divides North America into zones based on the average annual extreme minimum temperature. By consulting this map, individuals can select species that are genetically capable of withstanding the coldest expected temperatures in their region. The hardiness zone designation for Yakima, Washington, is currently Zone 7a.
Yakima’s Official Plant Hardiness Zone
Yakima is officially located in USDA Plant Hardiness Zone 7a, according to the most recent map updates. This designation is based on long-term climate data collected across the nation. The zone classification represents a shift, as older maps previously placed Yakima in the slightly colder Zone 6b. This change reflects updated data collection and a gradual warming trend in the region’s winter extremes. Located in the semi-arid, rain-shadowed valley east of the Cascade Mountains, Yakima has a distinct continental climate.
Understanding the Zone’s Temperature Metrics
Zone 7a defines a narrow range for the average coldest temperature recorded each year. This zone indicates that the average annual extreme minimum temperature falls between 0°F and 5°F (approximately -17.8°C to -15°C). The USDA system divides each major zone number into two subzones, ‘a’ and ‘b’, representing a 5°F increment. Therefore, 7a is the colder half of Zone 7, which spans from 0°F to 10°F. This metric is solely focused on winter survival and does not account for summer heat, rainfall, or the length of the growing season.
Practical Gardening Implications for Yakima
The Zone 7a designation means gardeners in Yakima can select a wide array of plants, shrubs, and trees that tolerate winter temperatures down to 0°F. Plants rated for Zone 7 and lower are reliably hardy and will likely survive the winter without special protection.
However, the Central Washington climate presents a dual challenge, requiring consideration of the region’s hot, dry summers. Yakima experiences a cold semi-arid climate with significant diurnal temperature variation and low annual precipitation.
Gardeners should plan their spring planting around the average last spring frost date, which typically occurs around mid-May. Starting seeds indoors approximately six to eight weeks before this date allows for healthy transplanting after the danger of a hard frost has passed. The intense summer heat and aridity necessitate selecting drought-tolerant plants or establishing robust irrigation. Successful plantings often include species adapted to this unique combination, such as ornamental grasses, lavender, and hardy fruit trees.