Date of Award


Degree Name

MS in Agriculture - Environmental Horticultural Science


Horticulture and Crop Science


Terry L. Vassey


ABSTRACT A Comparative Study of Three Growing Media and Four Plant Groups Under Extensive Green Roof Conditions in San Luis Obispo, California Todd A. Nelson Green roof growing media and plant species are critical factors when deciding on the best materials for a project. Growing media must be chosen in accordance with load bearing capacities of structures and water requirements of the plant material. Plant species must be able to thrive in the climate of the green roof and withstand a green roof’s harsh environment. The objectives of this research were: (1) to determine which of three extensive green roof growing media support the most growth of Sedum, a proven extensive green roof plant genus; and (2) to determine which of four plant groups provides the most media coverage under extensive green roof conditions. Sedum growing in a granular growing media blend with higher organic matter and larger particles provided more coverage than Sedum growing in a medium with smaller particles with lower organic matter and an experimental foam medium. Sedges covered the soil faster than Sedum, grasses, and Mediterranean species. These results will help green roof designers and landscape architects anticipate the plant growth rates during the first 36 weeks of new projects and choose more effective growing media blends. They can also observe the growth patterns of the plant groups to choose plant material that will achieve the functional objectives of a green roof more efficiently. These results are applicable to green roofs designed for moderate California coastal climates and regions with similar weather conditions.