Seed Germination in Green Roof Media


Cheng Chen

Document Type


Degree Name

Master of Science (MS)


Ag Science and Natural Resources

Date of Award

Summer 2013


Green roofs are an environmentally friendly roofing technology in use around the world today, and they provide multiple environmental and economic benefits, such as surface temperature reduction, reduced internal cooling needs, storm water management, and extended lifespan of roofing materials. Green roof substrates differ, both in composition and depth, based on type of roof, climate, and plant species. For plant survival and spread, many roofs rely on deposition and germination of seed. However, a discussion of seed germination in green roof media cannot be found in the literature. Given the coarse nature of green roof media, it is likely that germination percentages will be lower than in traditional mixes. For this study, we tested the germination of four wildflower species: Ox-eye daisy (Leucanthemum vulgare), Shasta daisy (Chrysanthemum maximum), yarrow (Achillea millefolium L.), Indian blanket (Gaillardia pulchella) and used pinto bean (Phaseolus vulgaris) (as a control) across five different substrates (peat/perlite/calcined clay, compost/sand/ expanded shale, compost/black dirt/expanded shale, compost/expanded shale, and peat/perlite). Substrates were analyzed to compare chemical and physical properties, including N, P, and K content, total porosity, water holding capacity, bulk density, and particle size distribution. A seed viability test was conducted prior to planting, and all test species were germinated in petri dishes. All seeds had a pre-test germination percentage of at least 80%, except L. vulgare which was excluded from the study. For the germination test, 25 seeds of each species were planted in each of the five media types, with each species/media combination appearing once per block. Germination was defined as seedling emergence from the media and monitored every seven days for 28 days. As expected, the large seeded pinto beans had the highest germination percentage (76.2%) across all media, compared to 43.4% for Indian blanket, 23.0% for Shasta daisy, and 40.4% for yarrow. Further, seed germination was lower in the green roof media, across all species. In the peat/perlite mix, 68.5% of seeds germinated, as compared to 44%, 39.3%, 37.5%, and 39.5% for the various green roof media. These data confirm that seed germination in green roof media should be expected to be significantly lower than in traditional growing media.


Derald Harp

Subject Categories

Agriculture | Life Sciences