"We've definitely seen the trend grow over the last 10 years or so," says Catherine Mahan, president of Mahan Rykiel Associates, a Baltimore landscape architecture firm that designed several area healing gardens.

A growing body of research shows that people feel better when they see gardens, and there are specific biological responses that account for that sense of wellbeing.

• A California-based research and advocacy group that believes good design makes better health care systems. The group sponsored a key study on healing gardens.

• Run by Roger Ulrich, leading researcher on the benefits of natural landscapes.