Thundercloud is a hybrid sedum with extremely pointed gray-green foliage. Plants emerge in spring in tight. dome-shaped mounds. In September, the plants bloom white. The short clumping plants reach about a foot tall and wide. It prefers a well-drained soil in full sun. Thundercloud is hardy to Zones 3 to 9 and can be planted in spring, summer or fall.from Intrinsic Perennial Gardens, Inc.