Evaluation of Vegetable Production on Extensive Green Roofs

Rooftop vegetable gardening is a production system in urban agriculture based on green roof technology. To broaden the scope of this practice, the use of relatively shallow substrate depths must be explored, since most existing flat roofs are unable to support much added weight. Three growing systemsa green roof, raised green roof platforms, and in-groundwere evaluated for vegetable and herb production over three growing seasons (2009-2011). Tomatoes (Solanum lycopersicum), green beans (Phaseolus vulgaris), cucumbers (Cucumis sativus), peppers (Capsicum annuum), basil (Ocimum basilicum), and chives (Allium schoenoprasum) were studied because of their common use in home gardens. All plants, except pepper, survived and produced biomass in all growing systems and yielded crops large enough for analysis in 2009 and 2010. Overall, yields and basil biomass were higher and of better quality in-ground during 2009, the only year irrigation was applied, and similar on the roof and platforms. Variability in success was partially due to annual weather variation with the greatest impact on cucumber. Yields of chive, a perennial crop, were not affected by growing system after the first year. Results suggest that, with proper management, vegetable and herb production in an extensive green roof system is possible and productive.