Effects of green roof growth medium depths on

Effects of green roof growth medium depths on Sedum immergrauch establishment. 1 2 3 4 5 6 Schaefer H. , K. Forrester , V. Jost , K. Luckett , S. Morgan , T. Yan and W. Retzlaff 1 2 3 4 1, 2 5 Department of Biological Sciences; Environmental Sciences Program; Jost Greenhouses; Green Roof Blocks, St. Louis Metal. Works, Inc. ; Department of Civil 6 Engineering; Department of Mechanical Engineering, Southern Illinois University Edwardsville, IL. 62026 (wretzla@siue. edu) ABSTRACT The purpose of my project was to determine the effect of various growth medium depths on the establishment of Sedum immergrauch in a green roof system. The shallower the growth medium, the greater the physical demands on the green roof plants. Shallow medium depth may lead to root damage from heat and frost fluctuations (Boivin et. al, 2001). Further, deeper medium depth may provide additional water for plant use during drought. A field study was conducted to determine if growth media depths of 5, 10, 15, or 20 cm influence plant establishment and survival of Sedum immergrauch in a green roof system. Analysis of the results indicates after ten weeks that there is no significant difference in plant growth, plant performance or roof coverage between 5, 10, 15, and 20 cm of growth medium in this green roof system. MATERIALS AND METHODS Roof Model Setup: Green roof models were set up in a completely randomized design with four replications of 5, 10, 15, and 20 cm of growth medium depth. All 16 green roof models are 70 cm x 70 cm wood frames with wafer board substrates and adhered EPDM roofing membrane. The models have sheet metal edging to retain the growth media. Testing Models: 4 with 5 cm of growth media with plants 4 with 10 cm of growth media with plants 4 with 15 cm of growth media with plants 4 with 20 cm of growth media with plants Plant Species: Sedum immergrauch Fertilizer: Isobutylidene-diurea, IBDU Nitrogen, a condensed product of urea and isobutylaldehyde. 1, 1 -Diureidoisobutane Figure 2. Plant growth index {(ht+diam 1+diam 2)/3} of Sedum immergrauch grown in 5, 10, 15, and 20 cm growth medium depths for 10 weeks. (n=20) Growing medium: Fine Arkalite – expanded clay Irrigation: By hand initially for the first two weeks as needed. On September 5, 2005, eighty Sedum immergrauch plugs were planted into the sixteen model green roofs. Each model contained five Sedum plugs randomly assigned to growth media depths of 5, 10, 15, or 20 cm. DATA COLLECTION The data collection methods in the field included measuring plant growth, plant performance, and roof coverage once a week for ten weeks. Figure 1. Green roof models with 5, 10, 15, and 20 cm growth medium depths at the SIUE Environmental Sciences Field Site. INTRODUCTION Today, building sustainable communities has become a global challenge that presents exciting new opportunities for the widespread use of green roofs. Green roofs help mitigate the impact of high-density commercial and residential development by restoring displaced vegetation (Van. Woert et al. , 2005). The type of roof planting that is of the greatest general interest and application in my project is called an “extensive green roof. ” An extensive green roof system consists of shallow soil depth, low weight, low maintenance, and wide plant diversity (Dunnett and Nolan, 2004). Although several plant species have been studied for potential extensive green roof utilization, the most preferred plants usually come from the genus Sedum plugs with established root systems may quickly spread out their roots and form dense vegetation in a green roof system. Sedums are most commonly known for being tolerant to extreme conditions of temperature, wind, sun exposure, and drought that exist on exposed rooftops. Plant species, growth medium depth, and water availability are all factors in determining the appropriate planting density of this species to achieve optimal green roof coverage. Having the drought tolerance characteristic is essential for the long life-span of an extensive green roof because of limited irrigation and shallow substrate depth. Deeper substrate depths may provide a greater water holding capacity that optimizes plant growth resulting in faster plant coverage (Van. Woert et al. , 2005). Therefore, growth media depths may alter Sedum immergrauch establishment on green roofs. Plant growth rate was quantified by measuring each plant’s height and width in two perpendicular directions. A growth index was calculated for each plant by averaging the three individual growth measurements (Monterusso et al. , 2005). Figure 3. Plant performance of Sedum immergrauch grown in 5, 10, 15, and 20 cm growth medium depths for 10 weeks. (n=20) Plant performance was quantified by rating each plant on a scale of zero to five, (0 - dead, 1 - stressed plant showing visible wilting or browning, 2 - plant that showed little change since planting, 4 - healthy plant exhibiting a large amount of growth, and 5 - exceptional growth and fullness) (Monterusso et al. , 2005). Roof coverage was quantified using a 6 x 6 circle coverage grid (each circle is 3. 8 cm in diameter) in 4 quadrants and counting the circles that have plants in them. All recorded data has been analyzed using SAS to determine if green roof growing media depth alters Sedum establishment (ANOVA for a completely randomized design, a < 0. 05). RESULTS AND DISCUSSION Growth Index: There was no statistical difference in plant growth between 5, 10, 15, or 20 cm of growth medium for 10 weeks (Figure 2). Performance: There was no statistical difference in plant performance between 5, 10, 15, or 20 cm of growth medium for 10 weeks (Figure 3). % Roof Coverage: There was no statistical difference in percent roof coverage between 5, 10, 15, or 20 cm of growth medium for 9 weeks (Figure 4). At the 10 th week measurement, percent roof coverage in the 5 cm depth was less than the roof coverage in the 15 cm depth. Fast establishment, fast substrate coverage, and low mortality are all desirable characteristics for Sedum immergrauch. Fast initial growth is important because the faster the plants cover the substrate surface, the fewer the number of plants required (Monterusso et al. , 2005). In this study, under this set of growing conditions, growth medium depths of 5, 10, 15 and 20 cm did not have any effect on the establishment of Sedum immergrauch. It remains to be seen whether, under different temperature and moisture conditions, medium depth will influence Sedum establishment in a green roof system. Figure 4. Percent roof coverage by Sedum immergrauch grown in 5, 10, 15, and 20 cm growth medium depths for 10 weeks. (n=16) CONCLUSION The primary goal during green roof establishment is to achieve 100% plant survival and 100% roof coverage as soon as possible. Different growth medium depths of 5, 10, 15, and 20 cm had no effect on the survival and growth of Sedum immergrauch in my investigation. No Sedum plants were lost in this study and, at the end of the 10 week study period, more that 30% of the green roof system was covered with plant foliage. These green roof systems will continue to be monitored for the next 2 years to assess plant growth, performance, and roof coverage. It remains to be seen whether growth medium depth will alter any of these characteristics following successful establishment. LITERATURE CITED Boivin, M. 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