Quercus suber aka Cork Oak

Quercus suber, the cork oak, is an evergreen tree. It belongs to the beech family, Fagaceae. Its home lies around the western and central Mediterranean. Its range includes southern Europe and parts of North Africa. It grows in forests and open woods. Portugal has named it the national tree.

Size reports vary with the source and growing region. American sources give 70–100 feet [21–30 metres], with equal spread. Virginia Tech gives a height of 65 feet [20 metres]. RHS lists heights above 39 feet [12 metres]. It lists spreads above 26 feet [8 metres]. Growth is slow, and full size takes decades. A short trunk supports thick limbs and a round crown. The trunk may split into branches near the ground.

Thick cork covers the trunk and main branches. The grey bark has deep cracks and reddish-brown grooves. Removing cork reveals a red layer beneath the bark. Young stems have grey hairs and pointed, reddish-brown buds. The leaves grow in an alternate pattern along the stems. Each leaf is simple, leathery, and oval to egg-shaped. The upper face is glossy and dark green. Pale hairs cover the underside of each leaf. The edges wave and may bear a few teeth.

Small yellow-green flowers appear in spring, with April reported. Male flowers form catkins; female flowers cluster beside the leaves. Long, narrow acorns have rough, shaggy cups. Sources differ on how much nut the cup covers. The acorns ripen in autumn within one growing season. Mammals eat them, and the tree gives wildlife shelter. Its leaves also feed moth and butterfly larvae. People can eat acorns after boiling or leaching removes tannins. RHS warns that eating this plant can harm dogs. NC State also warns of toxicity to horses.

Grow cork oak in full sun with good drainage. It tolerates several soil types and resists drought once established. RHS favours soil that drains well but holds some moisture. USDA ratings vary from zone 7 to zones 8–10. RHS assigns the tree its H5 hardiness rating. Its size suits parks, streets, and large gardens needing shade. Mature bark supplies cork for bottle stoppers and flooring. Growers harvest it again after the bark has regrown. Care needs are low, but pests and disease can occur. Aphids, scales, borers, leaf miners, and caterpillars may attack. Gall wasps can also affect the tree. Possible diseases include powdery mildew, honey fungus, and leaf spots.