Photo: Famartin, CC BY-SA 4.0 · Wikimedia Commons

Post Oak

Quercus stellata

Also called iron oak, cross oak.

A drought-hardy white oak of dry ridges and the Cross Timbers, with leathery, cross-shaped leaves, that can live 300 years or more.

RareDrought tolerantWildlife value

Type: Medium tree
Mature height: 35–50 ft
USDA zones: 5–9
Growth rate: Slow
Sun: Full
Soil moisture: Dry, Average
Grows wild in: Dry uplands and rocky ground
Native range: 28 states and the District of Columbia, north to New York, south to Florida and west to Texas
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Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Mississippi, Missouri, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Virginia, West Virginia and the District of Columbia
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Post oak is a white oak of dry uplands, abundant across the Southeast and South Central states and the most common oak in Texas. Its wood lasts in the ground, which made it the fence post behind its name. Even so, it is seldom planted in gardens. Of the three post oaks we grow, it is the upland one. Sand post oak stays smaller on deep sand, where post oak itself seldom grows, and Delta post oak takes the wet bottomlands that post oak cannot stand. Plant it once, on a dry, rocky or thin-soiled site, and leave it to grow for centuries.

Size, growth and what to expect

Post oak seedlings in Missouri averaged only 2.5 inches of height a year over six years. That is well under the foot a year our growth estimator gives a slow tree. Expect 35 to 50 feet with an equal spread. Mature trees in the Southeast stand 50 to 60 feet.

It flowers from March in the South to May farther north, and the acorns ripen in a single season, dropping from September through November. Trees begin to bear at about 25 years, with good crops every 2 or 3 years. The acorns are half to three quarters of an inch long. Turkeys, deer, squirrels, jays and wood ducks eat them.

It ranges from southeastern Massachusetts to central Florida and west to central Texas. A tree can live 300 to 400 years.

How to grow Post Oak

Post oak wants full sun and a well-drained soil on the acid side, and it makes do with poor, thin or rocky ground. It takes drought well once rooted, but flooding stresses or kills it, so keep it off wet ground. Set trees 35 feet apart, and keep each one 25 feet from a wall and more than 50 feet from overhead wires.

Saplings ship potted. Post oak roots resent disturbance, so plant it young and plant it once. Plant from leaf fall until bud swell, in a hole wider than the pot 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. White oak acorns sprout soon after they fall. Sow them on arrival, an inch deep, under hardware cloth.

Water every week or two through the first summer, then only in a long drought. Deer and rabbits browse young oaks, so guard each sapling with a tube or cage for its first three years. Once it is grown, keep fill, paving and heavy traffic off its roots, since it does not tolerate compacted or scraped soil.

The flowers are wind pollinated, and an acorn crop wants another oak nearby. As a white oak it suffers far less from oak wilt than the red oaks, but prune in the dormant season all the same. Chestnut blight can canker and kill post oak. Weevils spoil many acorns, and mistletoe may stunt a branch without killing the tree.

Heights and zones are typical ranges for the species in cultivation; local conditions and seed source shift them.

Sources (12)