Burr oak, also spelled “bur oak,” is a tree with many striking features, including crooked branches, large leaves and big acorns. It is a highly adaptable species of oak tree and a member of the beech family. The burr oak gets its name from the fringed cap that grows on its acorns, which is somewhat spiny. The tree has attributes that make it a desirable landscaping choice, with an ability to grow in dry conditions as one of its best characteristics.
The geographic range of the burr oak extends from portions of the East Coast into the Midwest and the Great Plains. The tree grows well into Canada and grows farther north than any oak in the Western hemisphere, according to the “National Audubon Field Guide to Trees.” Burr oaks often transition the hardwood forests of the East into the grassy prairies of the West, growing in large numbers in the areas between. The tree exists as far to the south as the coastal areas of eastern Texas.
Most burr oaks will grow to heights of 80 to 90 feet, but some that take hold in fertile soil can be much taller. The Utah State University Forestry Extension says that some burr oaks in the Ohio Valley may grow to 170 feet tall and have trunks with a diameter of 7 feet. What makes the burr oak so attractive, though, is that its spreading canopy of branches is almost as wide as the tree is tall. If you choose a burr oak for your property, be aware of this and place it in an appropriate place where it has room to grow.
Burr oak features a root system that runs deep and spreads out in such a way that it allows the tree to absorb any moisture in the surrounding ground. The leaves of a burr oak have a leathery texture, between five and nine separate lobes and are a dark green color. They are as long as 10 inches in some cases and give the tree a very full appearance before falling off in the autumn. The leaves lack any spectacular fall colors, typically turning a yellowish-brown or chartreuse shade.
The frilled acorns of the burr oak can grow to as long as 2 inches in parts of this tree's southern range, with those in northern states not attaining quite those lengths. Their odd cap, according to the Ohio Department of Natural Resources, gives it one of its nicknames, “mossycup oak,” as it seems to some people that it has a top part made of moss. Wildlife takes advantage of these acorns as a source of food. The acorns will ripen by the middle of autumn.
When planting a burr oak you should put it in an area that gets full sun or sun for most of the day, even though when the tree is young it has the ability to tolerate shady conditions. It will grow better if the soil is slightly alkaline rather than acidic. The large root system of a burr oak makes it a poor candidate for transplanting, so if you decide to take this course of action with one, do it when the tree is young and has yet to develop extensive roots.