Many plants are advertised or described as drought-tolerant, but what, if anything, does that tell us? Drought-tolerant where? Drought-tolerant when? Drought-tolerant if . . . what? By now, with unusually dry weather increasingly common worldwide, most gardeners likely are aware that drought itself may be defined in different ways, depending on one's perspective. Heteromeles arbutifolia (toyon) At the risk of oversimplifying, meteorological drought is lower than normal precipitation. Hydrological drought is lower than normal streamflow or groundwater levels. Agricultural drought is inadequate soil moisture for specific crops. Socioeconomic drought is insufficient water supply to meet demand. Ecological drought is insufficient
Global temperatures have been rising at least since the middle of the last century, and most projections anticipate that this trend will continue. Effects of warming vary from one region of the world to another but prominently include the likelihood that precipitation will shift from snow to rain in many snow-fed watersheds. It is also likely that snow will melt faster and run off earlier, changing the timing of peak streamflow. Snow is an important, even critical, seasonal water source for many regions with large mountain ranges, including most summer-dry climates. Snowpack accumulates in the mountains in winter when demand
Supplemental water is critical for gardens. Even the most enthusiastic native plant gardener recognizes the urban environment is not natural and cannot support a beautiful, healthy garden without some irrigation, especially in dry years.
We expect summers to be dry here in California. It’s a summer-dry or Mediterranean climate of wet winters and rainless summers. Gardeners learn to adapt and use plants that are native to summer-dry climates.