Unless you saw its acorns, you may not recognize the willow oak tree as an oak since its leaves are short, narrow and thin. Forming a rounded canopy, the willow oak (Quercus phellos) is one of the best oaks for gardens and parks and to provide shade along streets, according to American plantsman Dr. Michael Dirr. This species is appropriate for use in U.S. Department of Agriculture winter hardiness zones 6 though 9.
The willow oak's native range is across the southeastern United States. It grows naturally from southeastern New Jersery to South Carolina, across Georgia in a narrow band across the middle counties and then widespread from Kentucky southward to the Gulf of Mexico. The westernmost extent of this tree's native range is in the woodlands of eastern Texas.
Reaching mature heights of 40 to 60 feet and a canopy spread 30 to 50 feet, the willow oak is a large tree, but not as massive as many other oak species native to eastern North America. Old specimens in forests can reach 80 to 120 feet in height, according to the U.S. Forest Service. It sheds copious amounts of yellowy pollen from its male flowers in mid-spring as the new leaves emerge. The leaves mature to deep glossy green and range from 2- to 5-inches in length, but only 1/2-inch in width. In autumn these leaves turn a rich gold to golden-brown before dropping away. The acorns, which are reliably produced every year, are small and brown, merely 1/2-inch in diameter or slightly less. The branching structure of this oak, as seen in winter, is attractive and even.
The willow oak is among the faster-growing oak species native to North America, potentially growing as much as 2 to 3 feet of new branch tip lengths annually. It also, once its root system is well-established after planting, is extremely tolerant of summer heat and humidity, drought and other environmental stresses common to human landscapes, such as compacted or shallow soils, and restricted areas for root growth (although not an ideal situation). Dr. Michael Dirr also comments that it is not as messy as other oaks since its leaves are small and acorns not produced in such abundance as to require raking from lawns or sidewalks. This oak does not survive wildfires and is particularly susceptible to damage from acid rain, as reported by the U.S. Forest Service.
Plant the willow oak in a sunny location where it receives no less than 8 hours of direct sunlight daily so it develops a uniform, well-shaped branching structure. It is best grown in a fertile, moist but well-draining soil that is acidic in pH. Soils rich in organic matter help the tree grow faster while helping to retain soil moisture and provide nutrients.
This oak species provides acorn food to ducks, squirrels, deer and turkeys as well as blue jays and redheaded woodpeckers. Grackles, flickers, mice and flying squirrels utilize the tree for nesting or general habitat.
Besides being a good shade and street tree, the fast-growing willow oak is sometimes grown in plantations to supply hardwood pulp to make building materials. The U.S. Forest Service mentions it is a good shoreline stabilizing tree to plant on reservoir edges where water levels fluctuate seasonally.