ASHS 2025 Conference

Extensive green roof mediums are shallow with low nutrient content and oftentimes susceptible to rapid drainage, which results in the use of concentrated synthetic fertilizers that can have a negative affect on runoff water quality. Therefore, a study was conducted on ‘Sweet Hungarian’ pepper (Capsicum annuum) over three growing seasons to compare organic and conventional synthetic fertilizers at manufacturer recommended rates for their impacts on fruit yield, leaf chlorophyll content (SPAD), and plant vigor on a green roof having an expanded clay medium. The fast release synthetic fertilizer utilized produced the highest yield per unit fertilizer cost while the controlled release synthetic fertilizer had the highest overall yield but at much higher cost compared to other treatments. Bloodmeal had the highest yield among organic treatments and was similar to the fast release synthetic. Although SPAD was correlated with yield differences among treatments, plant vigor rating better explained these variations in yield. Pre and post growing season medium analyses revealed several interesting trends over the three-years of the study regarding pH, soil organic matter and nutrient contents that will be reviewed in detail. Additionally, an analysis of yield tradeoffs with fertilizer product costs among several popular organic and synthetic fertilizers for a nutrient-demanding crop grown in an extensive green roof environment will also be discussed. Green roof agriculture is a promising solution to enhance sustainability, especially where growing space is limited, but nutrient management is an important part of this system that needs to be sufficiently considered.