Bur Oak, Mossycup Oak
 

Mature Size, Growth, Longevity

Landscape size: 70-80' tall & wide. Has grown to over 100'. Weakly pyramidal form to oval, then developing a broad, spreading crown of very strong branches. Slow growth rate, less than 1' per year. Lives 300-400 years.

Native Range

Kentucky Native — Native from Nova Scotia to Pennsylvania, west to Manitoba and Texas, including most of Kentucky. Introduced 1811.

Flower and Fruit Details

Flowers are monoecious. Males in 1-2" yellow/green/brown catkins, just after leaf emergence, April/May. Fruits: large, 0.75 -1.5" acorns, broadly ovoid, downy at apex, with a deep cap, usually stalked, solitary. Acorn is 1/2 or more enclosed by a heavily fringed cap with fine, wiry, bristly burs, giving it a "mossy-cup" appearance, thus the 2 common names.

Leaf and Bark Features

Deciduous: Leaves are alternate, simple, obovate to oblong-obovate, 4-12" long, 2-6" wide, wedge-shaped at the base, glossy, dark green above, often grayish to whitish pubescent underneath. Shaped like a bass fiddle, much wider at top than bottom, with 2-4 pairs of lobes, and deeply cut sinuses in the upper middle. Petiole is downy, 1.25" long. Stipules around cluster of terminal buds. Dull yellow-green, yellow to yellow-brown fall color. Bark is rough, dark gray to gray-brown, with a deeply ridged and furrowed character. Young stems are stout, yellowish-brown, sometimes developing corky ridges.

Culture and Care

Difficult to transplant. Needs full sun. Very adaptable to various soils from sandy plains to moist alluvial bottoms. Tolerates clay, drought, heat & salt. Takes acid or alkaline soil, pH 4.6-8.0. More tolerant of city conditions than most oaks. Zones 3-8. Sensitive to soil compaction. Susceptible to periodical cicada, anthracnose, bacterial leaf scorch, basal canker, canker, leaf blister, leaf spots, powdery mildew, rust, twig blights, wilt, wood decay, shoe-string root rot, galls, scales, gypsy moth, lace bug, oak mite and others.

Strengths, Weaknesses, Other Facts

Good wildlife value. 4-season interest: Spring, summer, fall, winter. Too large for average home landscape. The specific epithet, "macrocarpa" means "large fruit", in reference to the large acorns. Songbirds eat the acorns.

Suggested Uses

Excellent tree for a park or large area.

Taxa and Plants of this Species at BCA