Family: Fagaceae
Common Name: Oak

This large genus of around 600 species comprises both deciduous and evergreen trees, which sometimes live to a great age and grow to an impressive size. Most are from temperate regions, but a surprising number are natives of tropical and subtropical regions, from Mexico through to Southeast Asia. They have alternate leaves, mostly lobed and leathery, but sometimes thin and glossy. The male flowers appear as yellow catkins in spring, while the female flowers are small and insignificant, and develop into the distinctive acorns, enclosed by a cup-shaped base. When ripe, the acorn (the nut) drops from this cup to the ground, from where it may be carried away by birds and animals. Grown for their handsome appearance and valuable timber, the oaks are ideal as street trees or for parks and very large gardens. The foliage of many deciduous types colours vividly in autumn. Evergreen species are often slower growers than the deciduous types.

Species

Q. canariensis, Algerian oak or Canary oak, zone 7, from North Africa, the Canary Islands and the Iberian Peninsula, will tolerate warmer conditions than many species. A semi-evergreen to 30 m (100 ft), it has coarsely toothed, shiny leaves that are glabrous on the undersides.

Q. cerris, Turkey oak, zone 7, from central and southern Europe and Turkey, is a very impressive, deciduous tree, growing to 30 m (100 ft). It has oblong, very coarsely toothed leaves, tinged with gray when young, and dark green and downy when mature.

Q. coccinea, scarlet oak, zone 4, from eastern North America, is a deciduous tree, to 25 m (80 ft), with deeply lobed, glossy, bright green leaves. The leaves colour a brilliant scarlet in autumn, remaining longer on the tree than those of other species.

Q. ilex, holm oak, zone 7, native to areas around the Mediterranean, is a dense, round-headed, evergreen tree with dark gray, scaly bark and leathery, rather narrow leaves, both entire and toothed. This species can be grown in exposed, coastal conditions. It grows up to 18 m (60 ft) tall.

P. palustris, pin oak, zone 5, from eastern and central United States, matures to a height of around 25 m (80 ft). It is a deciduous, graceful tree with pale green, deeply lobed foliage which colours red in autumn, remaining on the tree for some time, though the colour is often poor in warmer areas.

Q. robur, English or pedunculate oak, zone 5, is a massive, round-headed tree, growing between 12 and 30 m (40-100 ft) in cultivation, and possibly one of the most famous of the oaks. The shortstalked leaves have rounded, shallow lobes. The rich green spring foliage deepens in summer and changes to dull gold or brown in autumn. This species is the source of fine timber and one of Europe's most valuable timber trees. Cultivar 'Concordia', known as the golden oak, is one of the smallest, growing to only 10 m (33 ft). The golden yellow spring foliage persists into summer.

Q. rubra, red oak, zone 3, from the east of North America, is a deciduous species, growing up to 25 m (80 ft). The oblong leaves have large, triangular, pointed lobes. This species colours beautifully in autumn to a rich red-brown colour.

Q. suber, cork oak, zone 8, is the main source of commercial cork. An evergreen growing to 18 m (60 ft), it has ovate, lightly toothed or entire leaves, glossy green above, gray and downy beneath. The thick, rough, silvery gray bark yields the cork.

Q. virginiana, live oak or southern oak, zone 8, from the south-east of the United States and Mexico, grows up to 18 m (60 ft) tall. This beautiful species is a dense, evergreen tree of rounded habit. The oblong to rounded leaves are entire or sparsely toothed near the apex, glossy, dark green above and white and downy below. This species makes an excellent shade tree.

Cultivation

All oaks thrive on deep, moist, rich soils and like plenty of water in summer. Propagate from the acorns sown in autumn. Plant in tall containers, as they soon develop a vigorous taproot. Acorns can also be planted where they are to grow. If transplanted from open ground, leave a ball of soil around the roots, as the roots are slow to recover if left bare. Cultivars are grafted or budded onto the common oak.

Climate

Most oaks prefer a cool, moist climate, but there are species that enjoy warm to hot climates.