Planting improves heart rate, stress levels of mentally challenged adults

In the first experiment of the study, the heart rate variation (HRV) was measured in 30 mentally challenged people at a rehabilitation center in Daegu, South Korea. Researchers in the second experiment measured the cortisol levels of 20 mentally challenged people from a residential home in Yeongcheon, South Korea. Min-Jung Lee from the Department of Horticultural Therapy at the Catholic University of Daegu (South Korea) published the results of both experiments in a report in HortTechnology.

For the first experiment, subjects participated in four indoor horticultural activities: a pressed flower activity, flower planting, flower arranging, and topiary crafting. Participants' heart rate variation was measured five minutes before and five minutes after each horticultural activity was performed. The pressed flower group and the planting group showed a significant improvement in the standard deviation of the normal-normal (SDNN) interval heart rate variation measurements. The planting group's SDNN and low frequency (LF) significantly improved; a significant improvement in total power (TP) and high frequency was also observed. The flower arrangement group displayed a significant difference in LF, while the topiary group showed a significant difference in TP.

The second experiment used the same four horticultural activities, but collected participants' saliva in order to analyze their cortisol levels. Compared with the baseline measurement, the pressed flower group displayed a significant decrease in cortisol density from the first to the seventh day of testing, however no significant difference was observed on the fourth day. The planting group showed a significantly decreasing difference in cortisol density on day seven compared with day four. The topiary group continued to show a significant decrease in cortisol density at each cortisol collection after the first day of topiary activities.

Interestingly, the participants in the flower arrangement group showed increased stress (as measured by low frequency), and showed no great change in cortisol density. "We inferred that activities such as cutting stems with shears and arranging the cut stems in the exact location are difficult jobs for mentally challenged people," Lee said.

The topiary group exhibited a significant difference in total power, and not only had the most significant difference in TP but also had the largest significant decrease in cortisol density among the four indoor horticultural activities. Lee noted that topiary activities are thought to be fairly valuable in aiding emotional stability and vocational rehabilitation for mentally challenged people.

The research supports previous studies that show that touching and mixing soil affects the activity of the autonomic nervous system (ANS) and relieves stress. Planting activities resulted not only in the greatest change in mentally challenged people's ANS but also in a significant gradual decrease in cortisol density.

Lee concluded that planting activities are the most effective horticultural activity for stress relief and added that the extension of indoor planting activities to outdoor planting activities targeted for mentally challenged individuals will have a greater effect not only on vocational rehabilitation, but also on emotional stability.