By measuring the residents’ concentrations of cortisol hormone before and after the plants were added, the research team were able to see if the greenery had any impact on stress levels.
Cortisol levels change across the day. In healthy diurnal patterns, levels peak in the early morning shortly after awakening and drop to the lowest concentration at night.
Steeper daily declines indicate more effective regulation of circadian and hormonal mechanisms, which is a likely consequence of reduced stress.
Before the experiment, only 24% of residents had healthy cortisol patterns. Over the course of the year following the plantings, this increased to 53% of residents having healthy cortisol patterns.
Perceived stress levels decreased by 6% after the introduction of the plants.
Over half (52%) of the residents said their front yard helped them be happier, 40% said it helped them be more relaxed, and over one in four (26%) said it helped them be closer to nature.