Santa Fe Botanical Garden

Common name: bur oak

Family: Fagaceae (Beech)

Distribution: Central and Eastern United States, Southern Canada

Habitat: Bottomlands, riparian slopes, alluvial floodplains, woodlands, hillsides, sandy ridges

Hardiness: USDA Zone 3 (-40 to -30 °F)

Life form: Deciduous tree

Growing Conditions: The range of bur oak extends from the eastern Canadian provinces west to Manitoba and the tips of Montana and Wyoming, south through the north-eastern and north-central states to Alabama and Louisiana and as far west as Texas. It is most abundant in the Mississippi and Missouri River Valleys and around the Great Lakes. It is a pioneer tree in the West, sometimes forming pure stands where it borders and invades prairie grasslands. In eastern North America, it is widely distributed in a variety of habitats including moist bottomlands, riparian slopes, alluvial floodplains, open woodlands, dry hillsides, sandy ridges, and prairies. It usually grows on limestone or calcareous clays, but tolerates a wide variety of conditions, including nutritionally poor dry sands as well as poorly drained and sometimes inundated conditions. It thrives in loam soils with a medium amount of water. However, it is one of the most drought-resistant oaks and is our most cold-tolerant oak. It grows in sun, part shade or shade, but mature trees are usually shade intolerant. Bur oak is monoecious and dichogamous, and self-pollination occurs rarely, if at all. In most, but not all, years it produces large acorn crops (masting). Acorn production may not occur until 35 years of age, but trees continue to produce seeds until at least 400 years of age. Bur oak is planted for shade, as a specimen tree, and for shelterbelts.

Description: A mature bur oak can have a trunk 40 or more inches in diameter, with its crown wider than the tree is tall. The tree tends to be shrubby at the northern and eastern limits of its range. The thick, dark gray bark has corky ridges and deep vertical furrows. Gnarly branches also have corky ridges. The leaves are broadly club-shaped, with rounded lobes, fine hairs on the lower surfaces, and 4-8 inches long and 2-6 inches wide. The leaves turn golden brown in autumn. The acorns are ½ -1 inch long, set in fringed cups. Greenish strings of pollen form catkins (clumps) at the terminal buds of the previous year’s branches. Green female flowers grow from the leaf axils of new growth.