Willow Oak

Size, growth and what to expect

Willow oak grows fast, about 2.75 feet a year in our growth estimator. Planted willow oaks averaged 46 feet tall at 17 years. Expect 40 to 75 feet with a crown 25 to 50 feet wide, and wild trees reach 80 to 120 feet.

It flowers from February to May, about a week before the leaves open, and the acorns ripen from August to October of their second year. Trees bear from 15 to 20 years old, with a good crop nearly every year. The acorns are under half an inch long, nearly round and often striped, among the smallest of any oak. Ducks, turkeys, deer, squirrels and blue jays eat them. The narrow leaves turn yellow to russet in fall.

It grows wild on the Coastal Plain from New Jersey and southeastern Pennsylvania to northern Florida and eastern Texas, and up the Mississippi Valley to southern Illinois and Kentucky. Its home is the ridges and flats of river bottoms that flood in winter but drain fast. Pennsylvania and New York list it as endangered, and Illinois as threatened, at the edges of its range.

How to grow Willow Oak

Willow oak wants full sun or light shade and a moist, acid soil, at its best a deep silt or loam over a water table 2 to 6 feet down. It takes clay, poor drainage, salt and city conditions. On alkaline soil its leaves yellow, so plant it only on acid or neutral ground. It takes flooding in winter and spring, but standing water that never drains kills it. Set trees 25 feet apart, and keep each one 25 feet from a wall and more than 50 feet from overhead wires.

Saplings ship bare-root or potted. Willow oak transplants easily, but it is said to move poorly in fall, so plant dormant saplings in late winter or early spring. Dig a hole wider than the roots and no deeper. Set the root flare at the soil line, put the native soil back in, and keep the mulch clear of the trunk. Red oak acorns need a winter before they sprout, and they die if they dry out. Sow them in fall half an inch deep under hardware cloth. For spring, hold them damp in the refrigerator for 30 to 90 days first.

Water every week or two through the first summer, then only in a long drought. Deer browse willow oak, so guard each sapling with a tube or cage for its first three years. Keep fill soil off the roots, since as little as an inch can kill an oak. Prune out double leaders while the tree is young, in the dormant season, to build one strong trunk.

The flowers are wind pollinated, and an acorn crop wants another oak nearby. A late freeze after the flowers open kills them, and the tree sets no second bloom that year. As a red oak it can catch oak wilt, so prune only in the dormant season, to avoid the beetles that spread it. It resists most pests, though borers attack weakened trees and weevils spoil some acorns.