River Birch

River birch (Betula nigra, Betulaceae) is a fast-growing deciduous tree native to the eastern United States, from Massachusetts to Florida and west to Missouri and Kansas. It reaches 40 to 70 feet tall with an upright, often multi-stemmed form. The signature feature is exfoliating bark that peels into papery plates, exposing inner bark ranging from gray-brown to cinnamon or reddish-brown, with considerable color variation between individuals. Rhombic-ovate leaves (4 to 9 centimeters) are doubly serrate with lustrous medium to dark green upper surfaces. Fall color is yellow but brief.

River birch thrives in full sun on moist to wet, acidic soils (pH 3.0 to 6.5), hardy in Zones 4a to 8b. It tolerates periodic flooding, clay soils, and urban conditions, with moderate tolerance of anaerobic soils and a minimum root depth of 20 inches. It is a short-lived pioneer species with high water needs. Documented diseases include rust, canker, and wood decay; pest associations include bronze birch borer, birch leafminer, aphids, and oystershell scale. The cultivar 'Heritage' (syn. 'Cully') is widely planted for its tan to creamy-white bark and reported resistance to bronze birch borer. 'Fox Valley' offers a dwarf form at 10 feet. River birch is a larval host for Mourning Cloak, Dreamy Duskywing, and Eastern Tiger Swallowtail butterflies.

Recommended replacement for B. pendula in Puget Sound landscapes. Highly resistant to bronze birch borer (0% rhododendrin; Santamour 1990, 1999). Heritage (‘Cully’) is the standard cultivar and performs well here. Tolerates wet soils and clay common in Green River valley sites. Requires acidic soil (pH 3.0-6.5); iron chlorosis likely in amended or alkaline soils - do not lime or use alkaline composts near root zone. Chlorotic trees on high-pH sites will decline unless soil pH is reduced or supplemental iron is applied. Avoid pruning in spring (heavy sap bleeder); prune late summer through dormancy. Deep water through July-September dry period to prevent drought stress. Fox Valley (‘Little King’) dwarf cultivar (~10 ft) available for smaller spaces.

— Chris Welch, ISA Certified Arborist