- Lead scientist
- Dr Paul Alexander, RHS
- Partners
- Sheffield University, Forest Research, Vital Earth, Shire Minerals and Bioregional.
- Start date
- 2009
- End date
- 2011
- Keywords
Compost, Biochar, Green Roof, WRAP, RHS
- Benefits to gardeners
Green roofs can confer a range of environmental benefits including reducing rainfall run-off, reducing the urban heat island effect, improving air quality, improving building insulation and increasing building lifespan (Dunnett and Kingsbury, 2008) as well as delivering aesthetic benefits and increasing green space within urban areas. Green roofs therefore have a role in both adaption to, and mitigation of, climate change as well as contributing to sustainable urban development.
- The problem
Getter and Rowe (2006) identify a number of requirements specific to green roof substrates: they need to be lightweight, well drained but good at retaining water and nutrients and not readily decomposed over time. These parameters usually mean that otherwise useful organic materials such as compost made from green waste can only be incorporated at up to 15% by volume in green roof substrate mixtures. Increasing inclusion of green compost would provide opportunities for new types of green roof planting and would provide another sustainable application for this useful recycled material. There is therefore an urgent need to combine horticultural knowledge of plant growth media with the emerging discipline of green roof design to establish a robust understanding of the performance of green compost in this environmentally-friendly application.
- Approach
A two year experiment will be established at Deer’s Farm to examine the use of green compost in green roof substrate mixes. Different rates of green compost (>15%) will be incorporated and comparisons made with and without biochar. The experiments will be undertaken using randomised and replicated large trays. Five different types of calcareous grassland plants will be grown in the substrate mixes to examine their suitability for non-standard green roof substrates. Plant health assessments will include growth measurements and estimated leaf chlorophyll content to infer plant health during the experiment, as well as biomass measurements at the end of the experiment. Leachate will be collected at regular intervals for analysis and substrate structure will also be regularly assessed.
- References
Dunnett, N. and Kingsbury, N. 2008. Planting Green Roofs and Living Walls. Timber Press, Portland.
Getter, K.L. and D.B. Rowe. 2006. The role of extensive green roofs in sustainable development. HortScience, 41: 1275-1285.