Enhance your 
Southwest: Rain Cistern
Tucson, Arizona, USDA Zone 9
When we began designing the Sonoran Desert garden around our new home, we had to answer the most fundamental desert-gardening question: How do I water my plants? During an average year, my rain gauge registers around 12 inches of rain—enough to keep cacti and other succulents alive, but not enough to keep many of the desert perennial plants we love looking landscape quality. However, we’re also committed to water conservation, both by disposition and by mandate; the community we live in requires that we use only 55 gallons of water per person per day. (The average household in the United States uses around 175 gallons.) As it turned out, part of the answer to our water dilemma was right over our heads: each year, our roof could harvest thousands of gallons of rainwater.
I began constructing a system that would capture most, if not all, of the 8,800 gallons of rainwater we calculated would flow off our 1,500-square-foot roof in a normal year. I found a pair of corrugated galvanized steel culverts (normally used to channel water under roads) that were three feet in diameter and eight feet high, each with a 422-gallon capacity, and sunk them into cement beds in our back courtyard. I directed our rain gutters into them and, using off-the-shelf plumbing, I connected the culverts to my drip irrigation system. This way I could use rainwater when I had it, and potable water when I didn’t.
I felt like the CEO of my own water company. During summer storms that first year, I would go outside in my boxer shorts in the middle of the night to check the water level, a habit my wife, Deirdre, found mildly disturbing. But a shimmering circle filled with clean, cool rainwater is a sight I never tired of. During those storms, the culverts could fill up in only 15 minutes, and the overflow would run down the street like a river.
One problem presented itself—the culverts stood out like twin rocket ships in our yard. In a town known for the manufacture of cruise missiles and for its jet-fighter graveyards, we thought perhaps the gleaming steel culverts wouldn’t look too out of place in our garden. (And they did echo the corrugated metal roof of our adobe bungalow.) Still, we decided to soften the industrial look of the culverts with vines. We slid rusted circular trellises over each one and chose a Iush Sonoran Desert native, yellow morning glory (Merremia aurea), to plant around them. By midsummer, the culverts were engulfed by an abundance of bright yellow flowers.
Managing my own water supply has given me great respect for the plants that can hang onto dear life between the rains. Without those tough plants and the culverts to supply extra water, our gardening would be much more limited. The 8,000-odd gallons of rainwater we capture throughout the year leave us feeling less encumbered by water restrictions. Because of rainwater, we are free to garden.
WORTH GROWING: Yellow morning glory (Merremia aurea)
Heat-resistant in the extreme, yellow morning glory is a godsend for gardeners in truly hot climates. The vine will climb 20 feet or more in a season, and its three-inch-wide, trumpet-shaped flowers stand out like golden flying saucers against its deep green foliage. The plant dies back to the ground in most winters, but the tuber from which it grows is hardy to 15°F, and the plant recovers rapidly with the onset of hot weather. It prefers well-drained soil, but will grow faster with some supplemental water.
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