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), floodplains, 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 Right' 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 environment, 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 branches 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.

Since in its natural setting the pin oak often grows near water, pin oak acorns are important duck food and are especially loved by wood ducks. Biologists recommend planting pin oaks in duck-management areas. The nut within the acorns is also coveted by other water birds, songbirds, and ground birds, as well as small mammals like squirrels, chipmunks, and even deer.

But pin oaks might not be the best choice if you're planting a small residential space. When mature, they grow out of proportion to other plantings. However, they make a terrific specimen or shade tree for large yards and along streets, especially if you cut off the lower, drooping limbs that die off over time.

Pin oaks can also be used to create bonsai plants. After a cursory search on the Internet, however, I couldn't find any for sale. Although the wood is strong, heavy, and closely grained, pin oak has limited use for furniture-making because the wood warps and cracks badly in drying. Some is used for pallets and in general construction, because the straight trunks do make good poles and pilings. In some areas the wood is used for fuel.

Oak Wilt

Perhaps the greatest danger for pin oaks, especially those in native stands, is oak wilt, a systemic fungal disease of oaks, especially in the red oak family. This disease was first identified in Wisconsin in the early 1940s and has been slowly spreading throughout much of the country ever since. Oak wilt is a vascular disease whose symptoms usually start in mid-May to early June and continue throughout the summer.

Leaf damage is the earliest indication of oak wilt. Infected trees' leaves begin to lose their green tones, turning brown and yellow from the outer edges inward. As the disease advances, leaves begin to drop, sometimes while still green, starting from the ends of the branches. By the time symptoms are noticed-particularly in pin oaks-it's already too late to save the tree. Wilt symptoms progress rapidly over the entire crown, affecting lower branches last. Death usually occurs within a few weeks to a year.

This disease is frequently transmitted by underground root grafts; the places where the root systems of two adjoining oak trees actually fuse together to create a single root system. The disease is also transmitted by several insects and related pests, including fruit flies, beetles, borers, mites, and even squirrels. It sometimes spreads via tree-trimming tools.

Oak wilt disease is usually found in oak woodlots or suburban subdivisions built where native oak stands were present. The disease is rare in urban landscapes where pin or other oak species have been transplanted. Oak wilt has appeared in states from Kansas and Nebraska east to New York and from Minnesota south to Texas.

No effective control is known, and infected trees must be cut down and destroyed. Trees dying of oak wilt should not be used as firewood.

Officials in Minnesota, where oak wilt is a very serious problem, have found the disease to be more easily controlled through prevention rather than by trying to "cure" infected trees. The secret is to avoid any damage or wounding of a tree in the springtime, because the open wood can give access to the fungus that causes oak wilt disease. Pin oaks should be pruned only when they are dormant in the winter time, never in April, May, or June. If a tree suffers storm damage or needs to have some branches cut off, be sure to use tree paint to cover the wounds as best you can.

To slow the overland spread of oak wilt, some states have established harvesting restrictions on state land. Cutting forest stands that contain oak trees is prohibited between April 15 and July 15, the period when sap-feeding beetles responsible for spreading oak wilt are most active. These beetles are attracted to fresh tree wounds and can infect oak trees that have been damaged during logging operations.

While oak wilt is a problem in many states, it is still isolated enough to allow you to consider the pin oak a good option for planting when you have the right spot with the right conditions. AF

Jeff Ball writes from his home in Attica, Michigan. [TOP]