Evaluating Plant Brushing as a Strategy for Height Control in Edible Crop Species

Greenhouse growers producing edible crops can encounter specific challenges when optimizing growing conditions. One challenge is soft growth associated with rapid tissue expansion. Soft growth can lead to plants falling over or soft, floppy leaves. These plants can suffer from increased disease pressure and lower market value. Controlling plant height is one way of reducing soft growth. Outdoors, winds or other external forces can create mechanical stress on plants, triggering a naturally occurring plant hormone called ethylene that reduces plant growth. I conducted an experiment during the summer of 2017 in the MacFarlane Greenhouses at the University of New Hampshire to introduce mechanical stress to hydroponic leafy greens, potted herbs, and seedling vegetables to test whether that stress would lead to reduced growth. I used an automated boom to brush plants with light plastic every hour and compared the growth of the brushed plants with the growth of plants that were not brushed. I found that the effects were species-dependent, with basil, sage, and tomato showing the greatest reductions in plant height. We also found that all brushed species showed a total reduction of shoot growth, and no significant difference in quality as defined by “leaf greenness.