Trees, shrubs and herbaceous perennials suitable for landscapes in the Panhandle must tolerate average annual minimum temperatures in the 0 to minus 10 degrees Fahrenheit range. Using U.S. Department of Agriculture plant hardiness zone designations, that correlates to zones 6a, 6b and 7a. USDA zones provide guidance for selection of plant materials only based on survival of winter cold. The presence of soil moisture or the effects of drying winds across the Panhandle can still kill plants even though planted in the appropriate USDA zone.
For precise data on climate, soils and USDA zone ratings in the Panhandle, contact your local cooperative extension office. Horticultural agents disseminate information from Texas A&M University to inform residents with up-to-date data and recommendations on horticultural topics. The far northwestern counties, including the town of Dalhart, are located in the coldest USDA zone 6a. In the extreme southeastern part of the Panhandle, around Happy and Clarendon, it's slightly warmer and rated USDA zone 7a. Much of the central parts, including Amarillo, remain in zone 6b. If you choose to use Sunset climate zone designations, the entire Panhandle lies in zone 10 -- the high desert of Texas.
The Growing Season
The growing season spans the time between the last spring frost and the first frost of fall. Knowing the frost dates in your part of the Panhandle helps you schedule planting annual flower and vegetable crops based on their abilities to survive frost. The last spring frost occurs around April 15 in extreme southeastern counties, about April 21 to 30 in central areas and by May 10 in the far northwest. In autumn, the first killing fall frost happens in late October in the northwest and progresses farther southeast by November 15.
Annual Crop Types
Grow cool-season flower and vegetable crops in spring and fall in the Panhandle when temperatures range between 25 and 70 F. Pansies, kale, lettuce, spinach, peas and cabbage grow best in the cooler months and tolerate frost. Conversely, once frost no longer occurs, grow heat-loving crops such as Madagascar periwinkle, moss rose, pentas, tomato, watermelon, squash, corn and peppers. Your local cooperative extension office will provide specific information on cultivar names or precise planting times suitable to your location.