Sourwood

Sourwood (Oxydendrum arboreum)

Sorrel Tree, Lily-of-the-Valley Tree

Full to part sun, medium to moderately dry moisture, drought-tolerant once established, prefers well-drained acid loam, does not tolerate alkaline or wet soils, pH 4.5–6.0.

25–50 feet tall by 15–25 feet wide; small, white, urn-shaped flowers in drooping panicles 15–25 cm long in July–August; fruit is a small 5-parted capsule that persists through winter. Growth rate slow.

Native region: Scattered across Tennessee with greatest concentration in Middle and East Tennessee upland forests; common on acidic, well-drained slopes of the Eastern Highland Rim and Cumberland Plateau.

Oxydendrum arboreum is the sole species in its genus and a member of the Ericaceae (heath family). The mid-summer white flower panicles, combined with brilliant red to purple fall color that often develops weeks before neighboring trees, make it one of the most valued four-season native ornamentals in the South. Sourwood honey, produced by bees foraging on the July–August blooms, is regarded as one of the finest American monofloral honeys. The species requires strongly acid soil — pH above 6.5 causes iron and manganese chlorosis, which can be severe and persistent. In Middle Tennessee, it performs best in the Eastern Highland Rim counties where sandstone-derived acid soils are common; alkaline limestone-influenced soils in the Central Basin are generally unsuitable without significant amendment. No serious insect pests; Phytophthora root rot occurs in poorly drained sites.