Overcup Oak

Size, growth and what to expect

Overcup oak gains height more slowly than many of its bottomland neighbors, and its trunk adds 2 to 2½ inches of diameter in 10 years on an average site. Our growth estimator still models it at roughly a foot and a half a year in youth on an average site, as it does any medium tree. In a yard expect 40 to 60 feet, and wild trees on river bottoms reach 60 to 90 feet with trunks 2 to 2½ feet through.

The acorns are ½ to 1 inch long, broader than they are long, and the scaly cup can cover the nut entirely, hence the name. They sprout in spring once the floodwater recedes. A tree can live about 400 years. Most begin to decline at 80 to 163 years. Of the few trees dated by their rings, the oldest so far reached 329. It flowers from March to May as the new leaves appear, and the acorns ripen in September and October and fall soon after.

It grows wild from Delaware and Maryland south to Georgia and northwest Florida, west to east Texas and up the Mississippi Valley to southern Illinois and Indiana, on poorly drained clay of river floodplains.

How to grow Overcup Oak

Overcup oak wants full sun. It is at home in soil that floods or stays wet for weeks, including heavy clay, and once established it also tolerates an ordinary lawn and summer drought. Its crown spreads about two thirds as wide as tall, so give it 25 feet from a house and keep it clear of overhead wires. Set trees 40 feet apart.

Plant bare-root saplings while dormant, from late fall until buds swell, in a hole twice the width of the roots and no deeper, root flare at grade, backfilled with the soil that came out. Mulch a ring three inches deep, kept off the trunk, and skip the stake unless the site is windy. Acorns are unusual for a white oak in that they do not sprout in fall. Soak them for a day, hold them in damp peat in the refrigerator for 150 to 170 days and sow them in spring an inch deep. Or sow in fall under hardware cloth and expect germination in April or May.

Water deeply once a week through the first summer and in dry spells for two more; a tree from a flooded bottom still needs water while its roots are small. Deer browse and rub young oaks, so keep a tube or cage on for three or four years. Prune only to a single leader and to remove crossing limbs, in late winter.

Like other oaks, overcup oak is wind pollinated and needs pollen from another tree to set acorns, so plant two or more seedlings. Growth is moderate, faster on deep moist soil than on a dry bank. Acorns begin after 25 years or so, in good crops every three or four years.