WHITE OAKS FOR THE NORTH
Dr. Leonard Perry, Extension Professor
University of Vermont
White oaks are majestic trees for larger formal landscapes, as well as for natural landscapes. Many species are native to our country, with the main one recognized by several states.
One of the two main groups of oaks (along with the red or black group) is the white group. White oaks generally have leaves with smooth, rounded lobes. They tend to form a deep taproot, so are often difficult to transplant. They produce acorns every year. Hardy and common examples in this group include the true white oak (alba), swamp white oak (bicolor), bur oak (macrocarpa), chinkapin oak (muhlenbergii), and the English oak (robur).
The true white oak species, which lends its name to this group, has been named the state tree of Connecticut, Illinois, and Maryland. In addition, a white oak in Hartford until the mid 1800’s figures in Connecticut history as the Charter Oak, and is depicted on their state quarter. The Wye oak in Maryland, when it was felled in a thunderstorm in 2002, was the largest white oak in America and was estimated to be 460 years old. The Wye oak had reached 96 feet high, 119 feet wide, and the trunk had a circumference of 30 feet!
Most round-shaped white oaks reach 50 to 80 feet high, and 60 to 80 feet wide in landscapes with age. But since they are slow growing, they can be enjoyed even in smaller landscapes for many years. I particularly like them for their bluish-green leaves that turn an attractive purplish red in the fall and are held long into winter. The true white oak species tolerates a range of conditions, but wont tolerate compacted soils. This species, similar to the red oaks, is very important for furniture and fine lumber.
The swamp white oak is similar in many ways to the true white oak, but is slightly hardier, and as its name indicates tolerates more swampy or wet soils. Its leaves, too, are not as lobed as those of the white oak. Like many species in the white oak group, its leaves are velvety hairy on the undersides.
The bur oak also is called the mossy cup oak on account of its acorns enclosed in a cap appearing “mossy” or fringed. This is a spreading large tree, eventually getting 70 to 80 feet high and wide. But, as with the white oak, it is slow growing so can be enjoyed for many years in smaller landscapes. It might grow only 20 to 30 feet over a 20 year period. The large leaves, reaching up to ten inches long, give the tree a coarse texture. Leaves turn a yellowish fall color.
Chinkapin oak also is called the yellow chestnut oak on account of its leaves resembling those of the true chestnut tree. The leaves have pointed lobes, compared to the rounded lobes of the chestnut oak. It is a very adaptable tree to a range of soils from wet to dry, clay to sand. It does grow naturally on, and prefers, alkaline limestone soils. Its medium growth rate slows with age, reaching at maturity 40 to 70 feet high and 50 to 80 feet wide, or wider than tall.
The English oak, as its name indicates, is one of the few non-native oaks to our country. It originally came from the forests of Europe, as well as from western Asian and northern Africa. The species in this country is not as hardy as most native oaks, generally listed to USDA zone 5 (-10 to –20 degrees F). In some areas such as the Pacific Northwest it may be invasive.
Leaves of the English oak can get powdery mildew disease, although many cultivars (cultivated varieties) show resistance. It has more cultivars than most other oak species, several being upright or “fastigiate.” These upright selections may be found as 'Attention', 'Skymaster', or 'Skyrocket'. 'Concordia' is a golden-leaved English oak.
If you have a medium to large landscape, well-drained soil, and full sun, then you might consider planting one of these stately trees for shade or as a specimen. Even if you have a smaller landscape, plant one of the slow-growing trees to enjoy for several decades before they grow too tall. If you are building a home, try and save these native trees if they exist on your property. Or, look for white oaks whether on walks through woodlands or parks and gardens.
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