None - red oak has big pores, so all the root beer would leak Size of mature red oak. Return to Illinois Forestry. Quercus rubra The red oak is one of the largest and most important timber trees. To make things even more complicated, we need to look at individual tree value on a per unit basis. The twigs are small, slender, greenish brown to dark brown. One of the fastest growing of the oaks, it attains a to 80 feet and a diameter of two to three feet. Have seven to 11 toothed lobes that are separated by sinuses extending about halfway to the midrib.