Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont
Even if you do not have a medium to large landscape conducive to these trees, you should be aware of oaks as most are native to this country, and they make some of our most stately trees on public landscapes. They are so popular that they have been named the official tree of six states and one Canadian province, and the national tree of the U.S. Long lived, oaks symbolize strength and long life in many cultures.
Oaks (Quercus) generally have an upright, rounded, or
spreading habit. They may reach 60 to 80 feet or more high, with a
similar spread. Oak leaves are varying shades of green in summer.
In fall, some species have plain brown leaves, others have soft
colors of russet and bronze, and others have bright orange to red
leaves. Leaves are rather large, some up to eight inches or so
long, with points along the margins, lobes and indentations. Since
oaks cross freely in the wild, leaves of such trees may be hard to
identify. Most oak leaves are deciduous (they lose them in the
fall) and hardy to USDA zones 4 (-20 to –30 degrees F) or 5, but a
few southern species hardy to zone 7 are evergreen.
Oak flowers aren’t their main feature, having male flowers
hanging like fringe in “catkins”, the female flowers either single
or a few clustered in spikes. Some species produce many catkins,
which can be messy when they drop. The female flowers of course
produce the fruits which are the nuts most know as acorns. Most
also know these are a favorite winter food of squirrels, rabbits,
deer, some birds and other wildlife. Native Americans also ate
Oaks in general prefer a well-drained soil that is slightly acid,
but most except pin and Northern red oak will tolerate some
alkalinity. The leaves of these two will turn yellow, with green
veins, if the pH of the soil is too high. Give oaks full sun for
Since some species of oaks may be hard to find in nurseries, they
may be started from acorns, or collected from the wild. Just make
sure if collecting you do so legally. Pay attention to which
species transplant easily, and which are difficult because of a
deep taproot. Keep this in mind, too, when starting plants from
acorns. Those forming a deep taproot will need a deep container if
you don’t plant them directly in the ground.
There are two main groups of oaks. The red or black group has
leaves with pointed tips on divisions. This group generally has
fibrous roots near the surface, making them easier to transplant.
They produce acorns every one or two years. Examples in this group
are the scarlet oak (coccinea), shingle oak (imbricaria),
pin oak (palustris), northern red oak (rubra),
shumard oak (shumardii), and the black oak (velutina).
The white oak group generally has leaves with smooth, rounded
lobes. They tend to form a deep taproot, so are often difficult to
transplant. They produce acorns every year. Examples in this group
include the white oak (alba), swamp white oak (bicolor),
bur oak (macrocarpa), chinkapin oak (muhlenbergii),
and the English oak (robur).
Oaks are generally tough, surviving most pest or disease
problems. One serious and often fatal disease, more in the Midwest
and Texas, is oak wilt. The name is descriptive of the symptoms.
The black oak group seems more susceptible to this disease than
the white oak group.
On the other hand, white and chestnut oaks may be more
susceptible to the other serious disease, sudden oak death.
Luckily this disease, which was likely introduced to our country,
is being confined by strict government regulation and observation
to parts of the west coast. Sudden oak death also is prevalent in
England and parts of Europe. It is serious as this contagious
disease can destroy other species of ornamentals, such as
rhododendrons, as well.
The next time you walk in the woods, or visit a gardens or park, look for some of these stately trees. If you have enough space, consider adding one or more to your own landscape for shade and as a specimen tree.
Return to Perry's Perennial Pages: Green Mountain Gardener Articles-- your reliable source of gardening information for over 50 years.