Stacy Sodolak for The New York Times  Mark Simmons, an ecologist on the Mueller Prairie project. More Photos »  WITH 70 days of 100-plus temperatures so far and no rain in sight, Austin is in the grip of its worst one-year drought on record. And gardeners are quickly finding out which plants can survive brutal heat and drought.  Native trees like cedar elms and hackberries are dropping their leaves. Ash junipers in the Hill Country are dying. Shallow-rooted azaleas and crape myrtles are toast, and most lawns are brown, except for those watered by private wells.  Animals are suffering, too. Coyotes and rabbits are showing up in city gardens in search of water and food. Hummingbirds can’t find nectar because many plants aren’t flowering.  The first week of August, when daily temperatures climbed to 107 or so, a bison escaped from a ranch in Manchaca, on the southwest side of the city, and wandered into the Lady Bird Johnson Wildflower Center seven miles away, where it spent several days grazing in the savanna grasslands.  Gardeners are embracing those prairie grasses with equal enthusiasm because of their heat and drought tolerance. These natives can be found in many of the city’s lawns, ornamental gardens and even green roofs. Remarkably, these deep-rooted plants can adjust to shallow soils, helping to cool houses and absorb rain — when there is some.  “If we get a rain, these grasses will all turn green,” said Lars Stanley, 59, an architect and metal artist, standing on a roof planted with natives that covers the studio he built in East Austin with his wife, Lauren Woodward Stanley, 45, an architect. “It reduces our cooling level immensely.”  The grasses (blue grama, curly mesquite, little bluestem and sideoats grama) go dormant in a drought, a survival strategy that keeps their roots alive. But the prickly pear and Texas sedum the Stanleys planted, succulents that store water in their fleshy pads, looked remarkably fine.  A plain black-tar roof can heat up to 170 to 200 degrees, Mr. Stanley noted.  The plants on this roof, rooted in five inches of a stony mix that includes crushed decomposed granite, perlite, lava rock, rice hulls and a dash of compost teeming with micro-organisms, “should knock that temperature down 100 degrees,” he said.  “But they have to be green and evapo-transpiring to do that,” Ms. Stanley added. “We’re not going to water them in the midst of a drought.”  With its reservoirs half-empty and tributaries down to a trickle, the city is rationing water. And the Austin Water Utility is offering rebates of up to $5,000 for installing residential rainwater collection systems.  When it does rain here, it tends to pour, sheeting across hard surfaces and dry lawns to storm sewers. So the more rain that is channeled into tanks or slowed by porous driveways and terraced gardens, the better for the land, as well as the water table, because plants will filter pollutants before sending water on to underground springs and tributaries to the Colorado River.  On the roof over the Stanleys’ studio, rainwater is channeled down a wide gutter that feeds into one of four 1,500-gallon tanks on the two-acre property. “We use the condensate from our air-conditioning also,” Mr. Stanley said. “It fills up a five-gallon bucket every two days, which adds to the tank.”  Other designers, like Christine Ten Eyck, a landscape architect, are replacing asphalt driveways and other hard surfaces with permeable ones, like gravel or crushed granite, and replacing lawn with terraced beds filled with plants that not only can take heat and drought but also absorb and hold water.  “I’ve done it passively, instead of actively with a cistern,” said Ms. Ten Eyck, 52, standing by the live oaks in front of the 1950s bungalow in West Austin that she shares with her husband, Gary Deaver, 65. “The whole idea was to slow the rainwater down, because we’re about eight feet higher than the street.”
Inspired by a summer of relentless heat and drought, designers in Austin, Tex., are using native prairie grass to create landscapes that thrive in even the worst of conditions.