Trees for High Desert

 The term High Desert is almost synonymous, in a horticultural sense, with regions of potentially severe cold winter temperatures. In these desert locations cold hardiness becomes a critical consideration in tree selection and placement. Complicating this decision making process is the limited amount of data available on the cold hardiness of many desert species. Some of the most valuable information, especially for introduced desert tree species, come from field or real world observations of these species in landscape settings made in a number of varied locations. Such data, while useful, is not scientifically collected and does have serious limitations. Reports that a given species was undamaged at a particular temperature may not take into account microclimates or physical and environmental conditions that may have helped buffer the effects of cold temperature. Further, the reported or official temperature for a community or metropolitan may have been recorded at a significant distance from the observed tree and not really reflect the temperature around the tree. The lack of accurate data in the immediate vicinity of the tree can result in over or under estimating hardiness. Growth conditions, tree age and maintenance practices can further influence hardiness observations. Trees fertilized late into the fall, either directly (fertilizer applied to intentionally stimulate tree growth) or indirectly, (fertilizer applied to under-story shrubs or winter grasses) carry a lot of succulent, frost tender wood into the winter months. Freeze damage to these especially tender tissues does not give a fair appraisal of the trees innate cold hardiness. Tender tissues produced in response to heavy, inappropriate pruning may also be overly sensitive to cold injury. Lastly, while the majority of trees exhibit signs of injury within days of freezing some trees may take weeks or months to express symptoms, leading to false assessments of hardiness. With these limitations in mind, the following list was compiled from reported observations of selected species in varied locations in Arizona and Nevada.*