With an ever-expanding range of successful green roof plants to choose from, how do you make the most of the variety available in a cost effective, sensible way?
1) Are you creating a garden or a machine? Always have a priority list of exactly what jobs your green roof needs to accomplish before starting to design. This approach has been supported by experts at a recent research conference in Sheffield, and pioneered by Ed Snodgrass, the leading green roof plant grower in the USA
2) ‘Depth is king.’ I think this was coined by Jeff Sorrill at the Green Roof Centre. The most drought tolerant species will have a go in 80mm substrate but may require occasional irrigation in drier parts of the UK. 120-130mm is thought optimum depth for maximum biodiversity using smaller plants. 150mm + allows for some larger plants but can also encourage grass to get established, so may need more maintenance.
3) Diet sensibly. Your plants will be surviving in extreme conditions which will impact on their physical structure and sometimes push them to the limit. Therefore substrate nutrition should be carefully tailored to match their needs.
As always, the growing medium is crucial to the plants performance, and is even more important on the rooftop.