In the Atlanta area, willow oaks are often encountered as landscaping around malls, shopping centers, and other commercial property. They are also used in parks, golf courses, and other areas that can accommodate their eventual large size. This popular tree, stately as an oak but with narrow, long leaves like the willow, has been aided in its spread by having a shallow root system that makes transplantation easy. It is native and common to the eastern and south central United States, from New York to Florida and westward to Texas and Oklahoma. Preferring moist, acidic soils such as is found in bottom lands and along stream banks, this tree can adapt to many different types of soils. The willow oak has many interesting traits and uses.
The willow oak, Quercus phellos, gets its common name from similarities to the willow. Its long, narrow leaves are similar to the willow. As these leaves also resemble the shape of a pen, some have called this tree a pen oak. I did this when I was young, not knowing that a different tree is named pin oak. Another similarity of this tree to the willow is its fondness of water, and like the willow it can be planted to pull water from wet areas. The willow oak’s scientific name phellos is latin for the word cork. Because this tree has little cork in its bark, this tree was somehow mis-named. The true cork oak from which thick cork bark is harvested, Quercus suber, is native to southwest Europe and northwest Africa.
The champion willow oak in Atlanta is in Avondale 
Estates, with a height 112 feet, spread 126 feet, and trunk circumference 18 feet. Growth of the willow oak is medium to fast for an oak, up to 2 feet per year. One should allow for size and other traits when choosing where to plant. Bark on a young willow oak is dark gray and smooth. With age, it forms deep furrows and rough ridges. The inner bark is pink. In full sun, the tree has large, spreading limbs forming a balanced shape. In partial shade, limbs will reach for the sun and not appear so balanced. Branches are smooth, flexible and hard to break, and have thin, gray bark. As the tree prefers medium wet, well drained soils, it can be used to pull water from wet areas to make them more 
usable. This same quality of pulling water to itself can also be a negative, as in drier areas it can pull available water and nutrients from neighboring plants and trees. As can be seen in the last picture, the tree’s fibrous roots are shallow and often exposed, and they may damage mower blades. Roots also aggressively spread and can damage nearby pavements and structures.
Leaves of the willow oak are lanceolate and simple, with smooth edges and a bristle tip characteristic of the red oak family. They can grow to 5 inches long and 1 inch wide, appearing shiny dark green on top and slightly lighter and duller underneath. Autumn leaf 
color is yellow-brown or dull gold, with red tinges. These leaves are attached to petioles about ¼ inches long, and these petioles are clustered toward the ends of narrow branches, attached alternately. When leaves and acorns fall in autumn, they are small enough that they are not such a problem when raked.
The willow oak is known for heavy annual acorn production, beginning when the tree is about 15 years of age. Pendulous yellowish-green male and female catkins appear in April, as leaves emerge. Acorns are among the smallest of oaks, measuring 3/8 inches wide and ½ inches long, and they take 2 years to mature. A shallow cap covers almost the whole acorn top when developing, but when mature the cap 
covers only about ¼ of the acorn. The bottom has a hairy tip. The acorn is dark brown with longitudinal streaks, and the cap is light brown with a warty texture. Acorns mature in September and October.
There is much to like about the willow oak. It is a stately tree with fine foliage, great for ornamental and shade tree use in landscapes. Planted in problem wet areas, 
the tree can help pull water from the ground to make it more usable. Wood from the tree is used for pulp, but it is also used much as the red oak in cabinetry, furniture, interior trim, flooring, lumber and veneer. It is said that a decoction of wood chips or bark can be applied externally as an analgesic, and as a bath for aches, pains, sores, cuts and hemorrhoids. The tree produces heavy crops of small acorns, which is important food for ducks, squirrels, chipmunks, and other animals. The willow oak’s features serve us very well.
