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 in landscapes eventually reach 50 to
80 feet high, and 60 to 80 feet wide. 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 won’t tolerate compacted soils. This species,
similar to the red oaks, is very important for furniture and fine
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 other
white oaks. 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
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.
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