Stuck in an emotional funk after a personal loss, Janice Mawhinney couldn't muster the enthusiasm to tend her backyard garden in Toronto for three years. Then, inexplicably, one day this past spring, she found herself vigorously weeding again, her spirits slowly blossoming along with a long-concealed blue lupine, a pink and white bleeding heart, several Shasta daisies, and a host of other recovered plants.

As Mawhinney restored the garden, it in turn helped restore her. Now, "every morning I rush to look out at all the color through my bathroom window," says Mawhinney, a 58-year-old reporter at the Toronto Star. "In just a few minutes I feel refreshed."

Common sense and experience tell us that hiking in the wild or working in a garden can be emotionally restorative. Now, scientists are beginning to understand why: Gardening — or simply observing a lush landscape — holds a powerful ability to promote measurable improvements in mental and even physical health.

Building on the science, a new practice of horticulture therapy is sprouting. Increasingly, hospitals are using the insights of environmental psychologists to build small but elaborate gardens for patients, visitors and even stressed-out doctors. Some urban botanical gardens and health-rehabilitation centers are creating so-called healing gardens with horticultural-therapy programs that teach patients and the public about the recuperative effect the natural world has on the human psyche.

"If a researcher had seriously proposed two decades ago that gardens could improve medical outcomes, the position would have been met with skepticism by most behavioral scientists, and with derision by most physicians," says Roger Ulrich, a Texas A&M University professor and a leading researcher in the effects of environment on behavior. "We now have studies showing that psychological and environmental factors can affect physiological systems and health status."

One study published in June found that people who were exposed to nature recovered from stress more quickly than others who weren't; what's more, the positive effects took hold within just a few minutes. Ulrich's research has shown that hospitalized patients whose windows looked out at landscape scenery recovered from surgery more quickly than those without such access. Other studies have found that simply viewing a garden or another natural vista can quickly reduce blood pressure and pulse rate and can even increase brain activity that controls mood-lifting feelings.

A growing body of evidence suggests that humans are hard-wired not just to enjoy a pleasant view of nature, but to actually exploit it, much like a drug, to relax and refresh after a stressful experience. Our earliest ancestors, Ulrich theorizes, likely needed a way to swiftly recover from a traumatic experience such as a hunt, a battle or an attack from a wild animal. "You can imagine that those who could look out at the open savannah, seeing its safety and tranquillity, and quickly feel calm but also alert to their environment would likely have a survival benefit over others," Ulrich says.