Effects of Species Proportions and Fertility on Sedum Green Roof Modules

Abstract

<jats:p>Nursery producers are interested in supplying sedum (<jats:italic>Sedum</jats:italic> sp.)-vegetated modular units for the green roof industry. This research examined the influence of three rates of controlled-release fertilizer (CRF) (50, 78, and 108 g per unit of 15N–3.9P–10K, 8- to 9-month formulation) on production of modules containing one or two <jats:italic>Sedum</jats:italic> species. Six <jats:italic>Sedum</jats:italic> species were evaluated independently: ‘Angelina’ sedum (<jats:italic>Sedum rupestre</jats:italic>), gray sedum (<jats:italic>S. pachyclados</jats:italic>), ‘John Creech’ sedum (<jats:italic>S. spurium</jats:italic>), tasteless sedum (<jats:italic>S. sexangulare</jats:italic>), ‘Weihenstephaner's Gold’ sedum (<jats:italic>S. kamtschaticum</jats:italic> var. <jats:italic>floriferum</jats:italic>), and white sedum (<jats:italic>S. album</jats:italic>). The species were then paired as follows: white sedum/‘John Creech’ sedum, ‘Weihenstephaner's Gold’ sedum/‘Angelina’ sedum, and gray sedum/tasteless sedum. For each pair, three starting proportions of cuttings were studied. In 8 weeks, the medium and high fertility rates produced significantly more units with at least 95% vegetation coverage than the low rate. In general, increasing the fertility rate increased the fresh weight at time of harvest, except for ‘Weihenstephaner's Gold’ sedum and tasteless sedum at the high rate, which developed “melt out.” Melted-out tissues turned brown, desiccated and detracted from the visual appearance of units. ‘John Creech’ sedum and white sedum had the greatest fresh weight followed by ‘Weihenstephaner's Gold’ sedum, ‘Angelina’ sedum, and tasteless sedum. Gray sedum grew substantially slower than all other species and had the lowest fresh weight. For white sedum/‘John Creech’ sedum units, harvest fresh weight proportions were similar to starting cutting fresh weight proportions. For gray sedum/tasteless sedum units, tasteless sedum outgrew gray sedum and gray sedum was barely noticeable in finished units. Harvest fresh weight and digital image analysis (DIA) of ‘Weihenstephaner's Gold’ sedum/‘Angelina' sedum units indicated that ‘Weihenstephaner's Gold’ sedum colonized units faster than ‘Angelina’ sedum, and had greater visual impact in finished units. Units started with 25% ‘Weihenstephaner's Gold’ sedum cuttings, the smallest proportion tested, were roughly 73% covered with ‘Weihenstephaner's Gold’ sedum at harvest. We recommend growers use the medium fertility rate to produce the most units with 95% vegetation or more in the least amount of time and with reduced risk of melt out. To achieve desired final species proportions, growers may need to adjust the ratios of cuttings based on uneven species vigor.</jats:p>

Fertilizer Rate and Type Affect Sedum-vegetated Green Roof Mat Plant Performance and Leachate Nutrient Content

“…This lower-leaf dieback may have been caused by shading from the dense top growth or poor air circulation. Barker and Lubell (2012) also observed a similar response in sedum after high levels of fertilization. Therefore, in the green roof mat system used in this study, fertilization at rates less than 15 g • m -2 N is recommended to prevent leaf dieback resulting from lush shoot growth.…”

“…Therefore, of all treatments, species composition in the 10 treatment remained closest to the original composition over time. Although Barker and Lubell (2012) suggest adjusting cutting ratios to influence species composition proportions, this study indicates fertility adjustments may also contribute to achieving desired Sedum spp. proportions on green roofs.…”

“…Green roof installations have been increasing annually in North America, growing by 115% in 2011 alone (Green Roofs for Healthy Cities, 2012). The increase in green roof installations is likely the result of the many environmental, economic, and aesthetic benefits of green roofs, owing to the success of green roof vegetation (Barker and Lubell, 2012;Berndtsson, 2010;Oberndorfer et al, 2007). Green roof plants play an important role in optimal green roof functions and contribute to green roof benefits (Dunnett et al, 2008;Morgan et al, 2012).…”

“…In addition, plant growth response to substrate fertility can be influenced by climactic stress conditions (Barker and Lubell, 2012;Clark and Zheng, 2012). Regional climate conditions (e.g., precipitation and air temperature) influence nutrient availability within, and nutrient loss from, the growing substrate.…”

Effect of Fertilizer Rate on Plant Growth and Leachate Nutrient Content during Production of Sedum-vegetated Green Roof Modules

“…With the increasing area covered by installed green roofs, production demand has also increased for green roof plants. Given the environmental, economic, and aesthetic benefits provided by green roofs (Barker and Lubell, 2012;Berndtsson, 2010;Getter and Rowe, 2006;Oberndorfer et al, 2007) as well as the billions of square feet for potential green roof installations in North America (GRHC, 2012), there is great potential for future growth of plant production for the North American green roof industry. In 2011, the majority of green roof installations were extensive green roofs (GRHC, 2012), which typically consist solely or mainly of Sedum spp.…”