Quercus alba typically reaches heights of 24 to 30 metres (80–100 feet) at maturity, and its canopy can become quite massive as its lower branches are apt to extend far out laterally, parallel to the ground. Trees growing in a forest will become much taller than ones in an open area which develop to be short and massive. The Mingo Oak was the tallest known white oak at over two hundred feet with a trunk height of 44.2 m (145 ft) before it was felled in 1938. It is not unusual for a white oak tree to be as wide as it is tall, but specimens growing at high altitudes may only become small shrubs. The bark is a light ash-gray and peels somewhat from the top, bottom and/or sides.

White oak may live 200 to 300 years, with some even older specimens known. The Wye Oak in Wye Mills, Maryland was estimated to be over 450 years old when it finally fell in a thunderstorm in 2002.

Another noted white oak was the Great White Oak in Basking Ridge, New Jersey, estimated to have been over 600 years old when it died in 2016. The tree measured 8 m (25 ft) in circumference at the base and 5 m (16 ft) in circumference 1.2 m (4 ft) above the ground. The tree was 23 m (75 ft) tall, and its branches spread over 38 m (125 ft) from tip to tip. The oak, claimed to be the oldest in the United States, began showing signs of poor health in the mid-2010s. The tree was taken down in 2017.

Sexual maturity begins at around 20 years, but the tree does not produce large crops of acorns until its 50th year and the amount varies from year to year. Acorns deteriorate quickly after ripening, the germination rate being only 10% for six-month-old seeds. As the acorns are prime food for insects and other animals, all may be consumed in years of small crops, leaving none that would become new trees. The acorns are usually sessile, and grow to 15 to 25 mm (1⁄2–1 in) in length, falling in early October.

In spring, the young leaves are delicate, silvery pink, and covered with a soft blanket-like down. The petioles are short, and the clustered leaves close to the ends of the shoots are pale green and downy, resulting in the entire tree having a misty, frosty look. This condition continues for several days, passing through the opalescent changes of soft pink, silvery white, and finally, yellow green. The leaves grow to be 127 to 216 millimetres (5–8+1⁄2 inches) long and 7 to 11.5 centimetres (2+3⁄4–4+1⁄2 in) wide and have a deep glossy green upper surface. They usually turn red or brown in autumn, but depending on climate, site, and individual tree genetics, some trees are nearly always red, or even purple in autumn. Some dead leaves may remain on the tree throughout winter until very early spring. The lobes can be shallow, extending less than halfway to the midrib, or deep and somewhat branching.

Quercus alba is sometimes confused with the swamp white oak, a closely related species, and the bur oak. The white oak hybridizes freely with the bur oak, the post oak, and the chestnut oak.

Detailed description

• Bark: Light gray, varying to dark gray and to white; shallow, fissured and scaly. Branchlets start out as bright green, later turn reddish-green, and finally, light gray. A distinguishing feature of this tree is that a little over halfway up the trunk, the bark tends to form overlapping scales that are easily noticed and aid in identification.
• Wood: Light brown with paler sapwood; strong, tough, heavy, fine-grained and durable. Specific gravity, 0.7470; weight of one cubic foot, 46.35 lbs; weight of one cubic meter 770 kg.
• Winter buds: Reddish brown, obtuse, 3 mm (1⁄8 in) long.
• Leaves: Alternate, 13–23 cm (5–9 in) long, 7.5–10 cm (3–4 in) wide. Obovate or oblong, seven to nine-lobed, usually seven-lobed with rounded lobes and rounded sinuses; lobes destitute of bristles; sinuses sometimes deep, sometimes shallow. On young trees the leaves are often repand. They come out of the bud conduplicate, are bright red above, pale below, and covered with white tomentum. The reddish hue fades in a week or less, and they become silvery greenish, white, and shiny; when mature, they are thin, bright yellow-green, shiny or dull above, pale, glaucous or smooth below; the midrib is stout and yellow, primary veins are conspicuous. In late autumn the leaves turn a deep red and drop, or on young trees, remain on the branches throughout winter. Petioles are short, stout, grooved, and flattened. Stipules are linear and caducous.
• Flowers: Appear in May when leaves are one-third grown. Staminate flowers are borne in hairy aments 6.5–7.5 cm (2+1⁄2–3 in) long; the calyx is bright yellow, hairy, and six to eight-lobed with lobes shorter than the stamens; anthers are yellow. Pistillate flowers are borne on short peduncles; involucral scales are hairy and reddish; calyx lobes are acute; stigmas are bright red.
• Acorns: Annual, sessile or stalked; nut ovoid or oblong, round at apex, light brown, shiny, 20–25 mm (3⁄4–1 in) long; cap is cup-shaped, encloses about one-fourth of the nut, tomentose on the outside, tuberculate at base, scales with short obtuse tips becoming smaller and thinner toward the rim. White Oak acorns (referring to Q. alba and all its close relatives) have no epigeal dormancy and germination begins readily without any treatment. In most cases, the oak root sprouts in the fall, with the leaves and stem appearing the next spring. The acorns take only one growing season to develop unlike the red oak group, which require two years for maturation.

Chemistry

Grandinin/roburin E, castalagin/vescalagin, gallic acid, monogalloyl glucose (glucogallin) and valoneic acid dilactone, monogalloyl glucose, digalloyl glucose, trigalloyl glucose, ellagic acid rhamnose, quercitrin and ellagic acid are phenolic compounds found in Q. alba.