Bur Oak

Bur oak is the toughest oak in North America, the species that grows farthest west into the Great Plains, surviving drought, extreme cold, grass fires, and the alkaline, heavy soils that kill lesser trees. The acorns are the largest of any native oak, fringed with the mossy, fringed cup that gives the tree its other common name: mossycup oak. The leaves are large, deeply lobed, and dark green, and the bark develops deep, corky ridges. It grows sixty to eighty feet with a massive, broad, spreading crown. Native from the Maritime Provinces to Montana and south to Texas.

In Western Washington, bur oak handles the heavy, poorly drained clay soils and occasional wet conditions that exclude many other oak species. It is one of the few oaks that tolerates alkaline soil, which makes it useful on sites with imported fill or concrete-influenced pH. The fall color is yellow-brown, not dramatic but acceptable. No significant disease or pest concerns are tracked. The growth rate is slow to moderate, and patience is required. For a large, long-lived, structural shade tree on a difficult site where other oaks cannot grow, bur oak is the most reliable species in the genus.