Fertilizer rate influences production scheduling of sedum-vegetated green roof mats

• Fertilizer application rate influences green roof mat production time.
• Sedum vegetative coverage and species composition respond to fertilizer rate.
• Fertilization at 25 g m−2 N is recommended for fall green roof mat production.

To investigate the influence of controlled-release fertilizer application rates on summer-propagated sedum-vegetated green roof mat production timing, unfertilized sedum-vegetated mats (control) were compared to mats fertilized in August 2011 with Nutricote® Total 18–6–8 100 day controlled-release fertilizer at 5, 10, 15, 20, 25, and 35 g m−2 N. Fertilization rate influenced vegetative coverage, shoot height, inflorescence height and canopy area, leaf greenness and weed biomass. Mat production was completed late fall, following fertilization at ≥25 g m−2 N, while production was completed early the next spring, following fertilization at <25 g m−2 N. Although vegetative coverage of individual Sedum spp. changed over the course of the study, acceptable overall vegetative coverage was maintained following fertilization at ≥25 g m−2 N throughout the 2012 growing season. Production time ranged from 63 to 300 days following fertilization at 25 g m−2 N and the control, respectively. Fertilization rate influenced inflorescence characteristics of Sedum spp. and maximum leaf greenness was calculated to occur after fertilization with 25.6 g m−2 N. Therefore, by adjusting controlled-release fertilizer rates, production of green roof mats can be accelerated or slowed to meet production scheduling timelines.