Dust sized Seeds from Oxydendrum arboreum Sourwood Lily of the Valley tree. This is one of the prettiest and underused trees in our landscapes. Hardy in zones 5 to 9 it grows 25 to 30 feet tall and wide. During the summer, its fragrant flowers appear three to four weeks. This is at a time when few trees are in bloom, making the sourwood stand out even more. After flowering has stopped, the seed capsules turn yellow, they then turn a light brown and remain on the tree for most of the winter. The young stems vary from olive green to burgundy red, and the grayish bark starts smooth but gets deep furrows as it matures. Sourwood should be grown in full sun to produce the best flowers and fall color. It prefers acidic soil that is well drained but moist