An old Ballard variety. The stiff, upright stems are topped with clusters of pure white double flowers that eventually open up to reveal with yellow centres. Deep green, glossy leaves are carried the length of the stems. This forms an upright clump.
Like many perennials the leaves may get some white mildew on them during warm autumns. This does not harm the plant, just disfigures it. Make sure there is enough air circulating around the clump.