Dr. Leonard Perry, Extension Professor
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. in 2004. Long lived, they 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 the nuts most know as acorns. Most also know these are a favorite winter food of squirrels, rabbitsk, deer, some birds and other wildlife. Native Americans also ate them.
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 best growth.
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 not planting 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, so are 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 recently, 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 many 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.
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