Amarillo, Texas, situated in the High Plains region of the Texas Panhandle, presents unique conditions for gardening enthusiasts. The primary point of interest is the USDA Plant Hardiness Zone. This standardized system determines which perennial plants can survive the region’s winter temperatures. Understanding this designation is necessary for successful agriculture and landscaping projects.
Amarillo’s USDA Plant Hardiness Designation
Amarillo’s official designation on the 2023 USDA Plant Hardiness Zone Map is 7a. The USDA system guides cold tolerance, basing its classifications on the average annual minimum winter temperature recorded over a 30-year period. Zone 7a specifically indicates that the region experiences average annual extreme minimum temperatures ranging from \(0^{\circ}\text{F}\) to \(5^{\circ}\text{F}\).
This measurement determines the lowest temperature a perennial plant must endure to survive the winter. The difference between sub-zones like 7a and 7b is only five degrees, but this small distinction can determine the survival of marginally hardy species. While the 7a classification provides a broad guideline, it represents an average, not a guaranteed minimum for any given year. Local factors, such as structures or elevation changes, can create microclimates that shift the effective cold tolerance within the city.
Selecting Plants Based on the Hardiness Zone
The 7a designation informs the selection of perennial plants, trees, and shrubs that can successfully overwinter in the Texas Panhandle climate. Gardeners should choose varieties rated for Zone 7 or lower to ensure they tolerate the \(0^{\circ}\text{F}\) to \(5^{\circ}\text{F}\) average minimum.
For example, native and adapted perennials like the Blackfoot Daisy or the classic Black-eyed Susan are reliably hardy, as are shrubs such as Boxwood and the brightly-stemmed Red Twig Dogwood. Hellebores, often called Lenten Roses, are a Zone 7 favorite because they offer blooms even during the late winter months, providing color when little else is active.
Conversely, any plant rated for Zone 8 or higher should generally be treated as an annual or brought indoors for the winter. Some tender perennials, such as certain varieties of Lantana, may survive in Zone 7a but benefit greatly from a protective layer of mulch or covering before a severe freeze. Even Zone 7a plants can be vulnerable to an uncharacteristic cold snap or a lack of insulating snow cover.
Chilling Hours for Fruit Production
Successful fruit production requires considering “chilling hours.” Chilling hours are the cumulative number of hours a plant’s dormant buds are exposed to cold temperatures, typically between \(32^{\circ}\text{F}\) and \(45^{\circ}\text{F}\). Fruit trees like peaches and apples need a specific number of these hours to properly break dormancy and set fruit in the spring. Amarillo often receives a moderate number of chilling hours, requiring the selection of varieties that specifically match the local requirement to ensure a successful bloom and harvest. Planting varieties with too low a chilling requirement can cause them to bud out too early, making them susceptible to a late-season frost.
Amarillo’s Climate and Time Zones
Beyond the plant hardiness map, the term “zone” can refer to broader climate and geographical classifications. Amarillo is situated within a temperate semi-arid climate, often classified as BSk under the Köppen climate system. This classification reflects the region’s dry conditions, characterized by hot summers and cold, dry winters.
Geographically, Amarillo is also within the Central Time Zone. Like the rest of Texas, excluding the far western corner, the city observes Central Standard Time (CST) during the winter months and switches to Central Daylight Time (CDT) in the spring and summer.