How much to water dry-climate gardens can be a puzzle. The consensus for lawns, the poster child for waste, is 1″/week. Beyond generic groupings into low, moderate, or high water use, the answer for plants is less clear and can challenge long-standing practices.
Let me wade into the morass with the Goldilocks principle. Applied to economics, medicine, astronomy, and other disciplines, I find it a fitting mindset for landscape irrigation too. As with the fairy tale porridge and beds, the optimum is towards the middle rather than at the extremes of a range.
Human nature being what it is though, when we see a wilted plant, we grab the hose. When it gets hot, we ratchet up the irrigation. Our lives run on weekly schedules, so we set controllers to run fixed days of the week (typically 2-3 times weekly for plants and 3-5 times weekly for lawns). Too much, too much, too much.
Drought-tolerant plants, likely the majority of dry-climate garden material, are not biologically conditioned for frequent water. Not only do they not need much, they don’t like it. Their native climates are arid with almost no rain or intense periods of rain followed by lengthy periods of dryness. Practice feast or famine: let soil dry for many days, and then when you do irrigate, water generously to get beyond surface roots.
In the same vein, water less during plants’ dormancy which counterintuitively can mean water less when temperatures rise. Many California natives such as Ceonythus thrive in winter rains but are intolerant of summer wetness. Strive to mimic natural habitats: irrigate during a species’ growth season and lighten up during its down times.
Many sources report over-watering is more common than under-watering, and watering too often causes more deaths and disease. While scientific studies are scarce, my garden’s sustainability transformation these past 4 years confirms those assessments.
Moral of the story? The Goldilocks zone is water infrequently, and when soil gets good and dry, water deeply.