When people think about "healing gardens" and other outdoor spaces at healthcare facilities, plants usually come to mind first: trees, shrubs, flowers, and grass. Plants are, certainly, what most differentiate a garden from, say, a parking lot. Greenery and the wildlife it attracts are also what most often engage garden users, invite them to stay longer, and keep them coming back. In addition, however, something as basic as air turns out to be important to healthcare garden users. Previous research has revealed that one of the primary reasons people step outside the healthcare facility is to "get fresh air" (Cooper Marcus