The popular pin oak - In Profile

American Forests, Autumn, 2002 by Jeff Ball

The native pin oak (Quercus palustris) suffers a bit from overexposure, much like an actor when he or she becomes a star and reaches celebrity status. People will either love you or hate you, but there are few emotions in between.

The pin oak's overexposure comes because, for cities and landscape contractors across a large part of the United States, it offers a number of advantages as a street tree. They've overused this hardwood, but for some very good reasons: Unlike many trees, pin oaks like clay soil and don't mind wet feet, two conditions not enjoyed by many other trees. The tree's shallow and fiberous root system makes it easy to plant and transplant, and it can tolerate air pollution better than a lot of other trees can. In fact, some estimate the pin oak to be the most common native oak for America's streets and parks.

With a maximum height of 50 to 75 feet, the pin oak is a bit large for traditional street tree applications unless the street planting strip is very wide. Its shape and size make the pin oak more suited to yards than streets.

Occasionally called Spanish oak, swamp oak, or water oak, Quercus palustris should not to be confused with the true water oak, Quercus nigra. The trees grow wild in swamps (palustris refers to marshes), flood-plains, and along riverbanks in the eastern and central United States. The species is hardy north to the Great Lakes and into southern New England (Zone 4) but does not grow well much farther south than Oklahoma or Virginia (Zone 7b). In its natural state pin oak is found growing with red maple, green ash, box elder, sweet gum, and elm.

The tree's handsome pyramidal shape has a somewhat unusual branch structure. Lower branches are pendulous or drooping downward, middle branches stick out horizontally, and upper ones are quite upright. The lower branches tend to die out as the tree matures, and many arborists cut them off. Choose the varieties 'Crown flight' and 'Sovereign' if you wish to avoid that problem; they have lower branches that do not droop.

Although pin oaks grow best in full sun, they will tolerate light shade. The preferred soil is coarse to fine, preferably hard, compact clay or silty clay loam. Unlike so many trees and other ornamental plants, pin oaks do not require well-drained soil. In fact, they demand wet soil. Pin oaks require lots of moisture; they prefer moist conditions and are sensitive to a lack of water. Young trees need extra water when first planted and in late winter before the ground freezes. Even mature, well-established trees will require supplemental watering during periods of irregular rainfall, and especially during prolonged drought.

FOLIAGE

Pin oak foliage is deciduous, though it seems reluctant to fall at the end of the season and persists on the trees well into February. The somewhat coarse leaves are 3 to 5 inches long and 2 to 5 inches wide. As a member of the red oak family, pin oaks have pointed leaves rather than the rounded leaves found in the white oak group. During the season the leaves are glossy dark green above and lighter green with tufts of hair along the veins beneath. In the fall, look for the trees to turn russet, bronze, or deep red.

Pin oaks produce drooping wind-pollinated male flowers called catkins; the female flowers come in groups of one to three just as the leaves begin to unfold. Two- to three-inch long yellow-green catkins appear in May just after the leaves emerge. By September or early October these give way to somewhat short, flattened red-brown acorns borne singly or in groups of up to four, which take two years to ripen. Once ripe, they fall off the tree from September into early December, but take note: Acorns do not appear until the tree is 12 to 15 years old.

Pin oaks are most comfortable in moderately acid soil (pH 5.5 to 6.5), and in fact will not tolerate alkaline soil, which causes serious chlorosis or yellowing of the foliage. If you must plant a pin oak in an alkaline enviromnent, acidify the soil before planting. You can add lots of sphagnum peat moss, then annually take steps to keep the soil acid at least as far out as the drip line. One way to do that is to mulch around the tree, at least in the first few years, with two or three inches of used coffee grounds. Check out a local restaurant or coffee shop as a source.

WHAT'S IN A NAME?

So where did the pin in pin oak actually come from? Some think it refers to the pyramidal growth habit of the tree. Others believe the name dates back to when the hard, straight-grained wood was cut into slender pins or pegs used to fasten the framework of buildings. Another group favors a reference to the pin-like stubby l)ranches left on the trunk as the lower branches droop and slowly die. A fourth school attributes the name to the small pin knots left in the lumber from the tree having numerous small branches.

MANY USES

Pin oak acorns provided food for native Americans, but their preparation took some effort. Being in the red oak family, the acorns contained a good supply of bitter tannin (for some reason trees in the white oak family don't have tannin in their nuts). You remove the tannin by leaching it out of the ground-up acorn meal but are left with a fairly tasteless mush for making pancakes or the like. I think I'll stick with a box mix, thank you.