Utilizing Sedum seeds as an installation method for green roofs through seed enhancement techniques

There are many benefits to installing green roofs including reducing storm water runoff and the associated problems with overloaded sewage systems, especially in high density urban areas. Green roofs also improve rain water and air quality and reduce the effect from urban heat islands by acting as thermal damper/evaporative coolers, which decrease heating and cooling costs and the subsequent pollution. Additionally, green roofs can extend the life of a roof and create natural habitats for birds and insects. They are also aesthetically pleasing which can improve people’s psychological state and productivity levels. One of the primary limitations to increased green roof installations in the United States is the cost, specifically, the high costs of labor to install the plants on the roof. The majority of green roofs today are installed using cuttings and/or plugs, nursery containers, vegetative mats, or modules. Each of these installation methods has advantages and disadvantages, but each requires a significant labor investment in growing and planting the roof. Due to the lack of their success on large scale green roofs, seeds are rarely used as an installation method, especially during the summer months; however, seed installations could potentially cost far less than other installation methods. Plant options for a green roof include various types of annuals, perennials, herbs, and succulents. Many factors influence plant selection for green roofs. Chief among them is a plant’s ability to withstand the harsh conditions found on a roof such as high temperatures and a coarse, quick-draining medium. Currently, Sedum species are the most commonly used plant for green roofs in the Eastern United States because they can tolerate and thrive in the aforementioned conditions. Seed germination requires optimal conditions that are seldom available on a green roof. In this dissertation, five Sedum species (Sedum acre, Sedum forsterianum, Sedum reflexum, iv Sedum selskianum, and Sedum spurium) were selected to test with seed enhancement techniques and hydroseeding. Without any previously published research available describing a successful seed enhancement technique, this study sought to create a seed priming technique using a water prime and a polyethylene glycol (PEG) prime. In addition, hydromulch was used in two of the studies conducted in 2011 to determine whether it held potential as a successful seed installation method. The five species were also tested for their viability over a period of time after being stored in cool, dry storage. The use of seed priming treatments in laboratory, greenhouse, and outdoor trials did not result in improved seed germination for most of the species. Although there was slightly higher germination in some of the primed seed species when compared to the control, the cost of the priming treatments would not be worth the small additional percentages gained in germination. Moreover, this research demonstrated that successful seed germination on a green roof is unlikely to occur without a treatment, such as hydromulch, which holds the seeds in place near the surface of the medium. The hydroseeded trials showed success in holding the seeds near the surface of the medium. In order to create a dense mat of Sedum species on a green roof, an ideal situation would be about 72 seedlings per square foot. Using the average germination rates from the control treatments (since they germinated as well or better than the treated seeds) of each seed species, numerical recommendations were made per square foot for hydroseeding a roof with each species. When the five Sedum species were tested for their viability over a specified period of time, it was determined that for Sedum acre, Sedum reflexum, and Sedum spurium species, the younger seeds germinated faster and had higher germination rates in a range of temperatures. Sedum forsterianum germination was very sensitive to increases in temperatures at any age of seed and would not, therefore, be recommended for use on a green roof. Sedum selskianum, on v the other hand, was the only one of the five species tested whose germination appeared to be unaffected by seed age.