Surprisingly there are several hundreds of species of oak widely distributed throughout the temperate and tropical regions of the world. Both evergreen and deciduous, they vary from small dense shrubs to large noble trees of great ornamental and timber value. With a few exceptions, most species succeed in any deep rich soil, whether alkaline or acid. While the majority of quercus species must be looked upon as collectors’ pieces, the following selection is very worthy of a place in gardens large enough to contain them.
Quercus cerris, the turkey oak, is notable for its elegance and rapidity of growth, and for its tolerance of chalk soils and seaside exposure. The variegated form, variegata, with leaves boldly margined creamy white, makes a striking variegated tree, ultimately of medium or large size.
The scarlet oak, Q. coccinea, is a large broad-headed tree from eastern North America, magnificent for six or eight weeks in autumn, when its glossy green leaves turn brilliant red. Its variety splendens is a fine form selected for the brilliance and reliability of its autumn colour.
Allied eastern North American species exhibiting similar, though less spectacular, qualities of autumnal leaf colour are Q. palustris, pin oak, a more elegant large tree with smaller, five or seven-lobed leaves, and Q. rubra, red oak, a vigorous, large, broad-headed species, its leaves are matt green turning russet red in the autumn and are larger than those of either Q. coccinea or Q. palustris. All three species are not successful on chalky or alkaline soils.
Q. frainetto ( conferta), the Hungarian oak, is a stately and handsome species worthy of wider planting. The deeply lobed obovate leaves are exceptionally large. It is successful on all soils.
Q. ilex, the holm oak or evergreen oak, is a Mediterranean species and perhaps the most majestic of all large hardy evergreen trees; its leaves are dark glossy green with grey downy undersides. In early summer the woolly young shoots and yellow catkins are a striking feature. At home in any well-drained fertile soil, the holm oak is excellent in maritime exposures. In small gardens its growth may be restricted by clipping — indeed it makes an excellent evergreen hedge.
Q. phellos is the willow oak, a handsome species for lime-free soils from the eastern United States of America. Usually forming a large round-headed tree, the willow-like leaves colour yellow and orange in autumn. A much renowned large, broad-headed tree, Q. robur (pedunculata), the common or English oak with its rugged bark, is notable for its longevity and for its timber value. Several varieties are particularly appropriate in gardens including concordia, golden oak, a small, very slow-growing form with bright golden-yellow leaves throughout spring and summer. This is a rare variety which is difficult to obtain but it is well worth the effort. Q. r. fastigiata, the Cypress oak, forms a large tree of dense, narrow, upright habit and fastigiata purpurea makes a smaller tree of similar shape, but with young shoots and leaves red purple throughout the spring and summer.