An ancient bur oak at Spring Grove Cemetery and Arboretum in Cincinnati, Ohio.
Bur oak is one of the largest of the oaks, commonly attaining a height of 60-80 ft (18-24 m), and occasionally reaching heights of more than 100 ft (30 m) and trunk diameters up to 6 ft (2m). (On very poor sites, bur oaks may survive for decades and never get more than 10 ft (3 m) tall!) Bur oaks have stout, crooked and gnarly branches. Trees grown in the open develop a broadly rounded crown as wide as the tree is tall. Grown under forest conditions, bur oaks have a tall clear trunk and an open, narrower crown of short branches. Smaller branches and twigs often have corky wings up to an inch (2.5 cm) wide. The bark is gray-brown to dark gray with prominent vertical furrows and ridges and resembles that of white oak (Q. alba).
Bur oak leaves are the largest of any oak: up to 12 in (30 cm) long and 6 in (15 cm) wide. They are roughly fiddle shaped with 5-7 irregular, rounded lobes. The terminal lobe, which has uneven crenate margins, is the largest lobe, taking up one-third of the leaf. The leaves are thick, leathery and rather rigid, crowded near the ends of the branchlets, and are dark green above and silvery wooly beneath. They turn dull yellow or yellowish brown before dropping in autumn.
The acorns can be as large (think: macrocarpa) as 2 in (5 cm) long, but are usually about half that. A little more than half of the nut is surrounded by the cup which has a conspicuous fringe of hairlike structures around its margin suggesting the common names bur and mossycup.
Location Quercus macrocarpa, or bur oak, usually occurs on exposed, often dry, uplands where limestone is near the surface. It often dominates sites with poor, sandy or gravelly soils, and sites with thin soil over a clay hardpan. It also grows in bottomlands where the soils are moist, but not flooded. Bur oak sometimes grows in pure stands along prairie edges and in the “oak openings” in the Great Lakes states. This is a tree of the Great Plains and Midwestern U.S. Bur oak ranges from the Texas Hill Country north to SE Saskatchewan, and west of the Appalachian Mountains to Ohio and southern Ontario. It is the commonest oak in Kansas and the Prairie states. Numerous isolated outlying populations occur around the main distribution, especially to the east and south.
Culture Light: Bur oaks need full sun. Moisture: Bur oak is one of the most drought tolerant of the oaks. It grows naturally where the average precipitation is less than 16 in (40 cm) per year, but it also occurs where precipitation is more than 50 in (125 cm) per year. Bur oak cannot tolerate flooded soils during the growing season, but it will grow in soils that are permanently moist. Hardiness: USDA Zones 3 - 9. Cold hardiness varies with origin, and growers in northern areas should select material that came from northern populations and vice versa.
Propagation: Bur oak is in the white oak group and its acorns mature in the autumn of their first year. They are capable of germinating right away; no pre-treatment required. Seedlings cannot survive in shade. Bur oaks begin to bear acorns around the age of 35 years and have been reported to continue producing acorns up 400 years of age, which is older than known for any other American oak. The heaviest mast crops occur every 2-3 years, with lesser crops in intervening years.
bur oak foliage
Bur oak is tolerant of a wide range of moisture and soil conditions and therefore is a very adaptable and useful tree in cultivation. Bur oak withstands city air pollution and smoke, poor soils and irregular watering. Although it probably is too large for most home lawns, bur oak is useful as a shade tree for larger landscapes and parks. Bur oak is a relatively slow growing and long lived tree, and makes an excellent street or avenue tree that will survive for centuries. Bur oaks are well adapted and rightly popular as park and avenue trees in the mid-western prairie region and Northern Plains of the U.S. and Canada.
The acorns of bur oak are edible and were eaten by Native Americans wherever the tree occurred, usually after treating with wood ash to remove the bitterness. White-tailed deer, red squirrels, native mice, wood ducks and other wildlife feed on the energy-rich acorns. The wood is tough and durable, and used for furniture, flooring, and construction. It resembles white oak lumber and is frequently marketed as such.
Bur oak is one of the largest and most picturesque of the oaks. The big leathery leaves, huge fringed acorns and deeply furrowed bark combine to create a bold statement in the landscape. Its massive structure is especially handsome in winter.
Bur oak is considered a pioneer species on the edges of fire-prone grassland prairies. The species is resistant to fire and sometimes dominates areas that are subject to repeated burning. In the absence of killing fires, bur oaks eventually give way to black oaks (Q. velutina), northern pin oaks (Q. ellipsoidalis), white oaks (Q. alba) and bitternut hickories (Carya cordiformis). Without even occasional fires, these trees eventually are replaced by the climax species sugar maple (Acer saccharum), basswood (Tilia americana) and American beech (Fagus grandifolia).