Willows are very useful in sewage processing and providing fuel for wood burning stoves. They grow very fast and are voracious feeders.
The large members of the willow family are usually seen as graceful waterside trees in gardens or landscape planting. Many are also conspicuous in their coloured winter bark which is more attractive if the trees concerned are pollarded or heavily pruned in spring every other year. In many species, the spring catkins are an additional feature. Most succeed in any deep, moist soil.
One of the most beautiful of large trees for landscape planting is the white willow, Salix alba, but the silvery colour of its silky hairy leaves and shoots varies from tree to tree. It is very successful in maritime conditions if planted in moist soil. In small gardens, several of its varieties are good value. S. a. chermesina ( britzensis, chrysostella), the red or scarlet willow, is particularly conspicuous in winter when the bark of twigs and young stems appears bright scarlet. Pollard every other year in spring to maintain this feature at its best.
S. a. sericea ( argentea), the silver willow, makes a small round-headed tree with consistently shining silvery leaves. It is considerably less vigorous than the type, and ideal for the small garden. The golden willow, S. a. vitellina, has brilliant yellow winter shoots which make it the perfect companion for S. a. chermesina. It should be similarly pruned every other spring.
S. chrysoconia (alba tristis, alba vitellina pendula, babylonica rumulis aureis) is a handsome, fast-growing, medium-sized weeping tree with a wide-spreading habit, extensively planted for its grace and beauty and particularly for its long golden-yellow weeping branchlets. Although ideal for public planting, it will quickly become too large for small gardens. Regrettably,
in country districts, this hybrid is also particularly prone to willow scab or canker (anthracnose) which is difficult to control on large trees. It is, however, worth spraying young trees two or three times during spring and summer with a liquid copper fungicide to reduce the incidence of this disfiguring disease.
The violet willow, S. daphnoides, makes a vigorous, upright-growing small tree, conspicuous in winter when its violet-tinted shoots appear over-laid with a white waxy bloom. The bright yellow catkins of male trees (var. aglaia) are a striking feature each spring.
The purple osier, S. purpurea, is rarely more than a tall shrub of loose open habit with attractive oblong leaves with blue-white undersides. However, its variety eugenei forms an upright-growing small tree with unusual grey-pink male catkins; in particular its variety, pendula, the purple weeping willow, makes an effective small weeping tree and is particularly suitable for small gardens and for sites where S. chryso coma would be too large.
The purple osier and its varieties are very worthy of garden space, and succeed even in dryish positions if need be.