Bur oak (Quercus macrocarpa) is a member of the broad white oak group (white, bur, chinkapin, swamp white, and post oaks). This group is characterized by having rounded lobes on the leaves and acorns which mature in a single growing season and sprout soon after they fall in the autumn.
Habitat: Grows on dry uplands and slopes. Found throughout the state.
Hardiness: varies with the species of oak tree ranging from zone 3 to 9
Growth Rate: Slow to Moderate
Mature Shape: Broad, rounded
Height: Varies with species. Often maturing between 50 to 75 feet tall. Capable of growing upwards of 100 feet.
Width: 40 to 70 feet. Varies with species
Site Requirements: Best growth in moist, well-drained soils. Adaptable to adverse soil conditions.
Leaves: Alternate, simple, lobed. Lobes have rounded tips
Flowering Dates: April - May
Seed Dispersal Dates: September - October
Seed Bearing Age: 35 years
Seed Bearing Frequency: Every 2-3 years
Seed Stratification: Prechill for 1-2 months at 34°F to 40°F
Bur oak exhibits more variation in its vegetative characteristics than any other oak species. The leaves are simple and arranged alternately on twigs. Single leaves have rounded lobes with a deep sinuses near the center of the leaf which appears to split the leaf in two. The leaves are dark green above and lighter green to gray below. Fall color varies from dull yellow, yellow green to yellow brown. The fall buds are clustered, 1/8-1/4 inch long and covered with pale, gray, fine hairs. The twigs are usually stout and yellowish brown and smooth at first and usually developing corky ridges with age. The bark of bur oak is dark gray, rough, and deeply ridged on older trees. The acorn is 3/4 to 1 1/2 inch long, enclosed half or more in a deep cup conspicuously fringed on the margin.
Bur oak is native throughout the state. It grows on a wide range of sites from stream terraces and floodplains to the driest of uplands. It is the most drought resistant of all the oak species mainly because of its extensive root system. In western Iowa it is the most abundant tree often forming pure stands; in the rest of the state is a less abundant member of the forest community growing with a variety of other species including other oaks, hickories, and aspen.
Bur oak is the prairie tree species because it was often associated with the prairie-forest border. Because of its relatively thick, fire-resistant bark and natural resistance to drought, it could compete successfully with the prairie grasses. These "oak groves" were favorite home sites for early settlers in Iowa.
Because of its slow growth rate and poor fall color, bur oak is not used extensively for landscape purposes. Because of its wide tolerance of site conditions and its tolerance to city environments, it could be used with success in landscape plantings.
Bur oak lumber has the same strength, hardness and durability characteristics as white oak but is often of less value because the trees develop more limbs and often are open grown. With good management, bur oak can produce high quality oak lumber and veneer.