Cold Tolerance of Ground Cover Plants for Use as Green Roofs and Walls

This study was conducted to compare the cold tolerance of seven ground cover species, Orostachys japonica, Sedum oryzifolium, S. kamtschaticum 'SG1', S. reflexum, S. rupestre 'Blue Spruce', S. spurium 'Green Mental', and S. takesimense, which have been used for green roof and wall systems in Korea. Plants were grown in 10-cm pots and 1 g of tissues at stem-end and crown of each species were kept under either light or dark condition, respectively. For cold tolerance tests, plants were initially left at 4 degrees C and linearly cooled to 0, -4, -8, -12, -16, and -20 degrees C at -2 degrees C.h(-1) rate. Low temperature injury and regrowth rates were visually evaluated and assessed by image analysis, respectively. The lethal temperature (LT50) of plant species was determined using electrolyte leakage measurements. S. reflexum was the most cold tolerant, showing the most survival at -16 degrees C, whereas S. otyzifolium and S. takesimense showed low temperature injury at -8 degrees C. Similar results were found with electrolyte leakage measurements at the stem end. For each species, the crown (Mean LT50: -12.15 degrees C) was more cold tolerant than the stem end (Mean LT50: -10.47 degrees C). In conclusion, S. reflexum and S. rupestre 'Blue Spruce' are recommended for planting in the central region of Korea during late fall and early winter, as they were more cold tolerant and showed more vigorous regrowth than the other tested plant species.