It's easy to see what people like about willows. They're fast growing and tolerate just about any type of soil. They're also the easiest of trees and shrubs to propagate: Just take cuttings at any time of year and stick them into moist soil. On the other hand, they are weak-wooded, short-lived trees, and their shallow, greedy roots make them hard to garden under and can invade water lines. Most are attacked by a host of pests (tent caterpillars, aphids, borers, spider mites) and diseases. Weeping willows do best near lakes and streams, although they can, with training, make satisfactory shade trees. Shrubby willows are grown chiefly for their showy catkins (this group is known as pussy willows) or colorful twigs, or to control erosion on riverbanks. Branches of pussy willows can be cut in bud in late winter and brought indoors to bloom. Willow species hybridize freely, resulting in much confusion of names in the nursery trade.
S. alba. WHITE WILLOW. Tree. Native to Europe, North Africa. Upright to 75100 ft. tall, 50100 ft. wide. Yellowish brown bark. Narrow, 112- to 4-in., bright green leaves are silvery beneath, may turn golden in fall. The following forms are valued for colorful twigs.
S. a. 'Tristis'. GOLDEN WEEPING WILLOW. Pendulous form, to 5070 ft. tall and wide (or wider). Young stems are bright yellow. Among the most attractive of weeping willows; may be sold as S. alba 'Niobe', S. babylonica 'Aurea', or S. vitellina 'Pendula'.
S. a. vitellina. Upright, with brilliant yellow twigs in winter. Can grow to tree size, but cutting back gives best color display: Lop to 1 ft. high yearly, just before spring growth begins. Stems may grow 8 ft. in a season. 'Britzensis' and 'Yelverton' have red or orange-red winter stems.
S. babylonica. WEEPING WILLOW. Tree. From China. To 3050 ft. tall and wide (or wider). Longer (3- to 6-in.) leaves, more pronounced weeping habit than S. a. 'Tristis'. Greenish or brown branchlets. This is a popular lawn tree, but keep its size in mind; planting anywhere near the house or a driveway, walk, or patio is usually a mistake. Be sure to give it moist soil, as it quickly becomes disconsolate and ratty looking in dry soil. 'Crispa' ('Annularis'), ringleaf or cork-screw willow, has leaves curled into rings or circles; it is somewhat narrower than the species.
S. caprea. GOAT WILLOW, FLORIST WILLOW. Shrub or tree. Native from Europe to northeastern Asia. Grows to 1525 ft. tall, 1215 ft. wide. Broad, 3- to 6-in.-long leaves are dark green above, gray and hairy beneath. Before leaf-out, male plants produce fat, woolly, pinkish gray catkins about 1 in. long. Can be kept to shrub size by cutting to ground every few years. 'Kilmarnock' (a male plant) and 'Weeping Sally' (its female counterpart) are two selections that will naturally sprawl on the ground; they are more effective grafted or staked to form small weeping trees 68 ft. tall, 6 ft. wide.
S. discolor. PUSSY WILLOW. Shrub or tree. Native to eastern U.S.; an old favorite in the South. To 1525 ft. tall, 1215 ft. wide. Slender, red-brown stems; bright green, 2- to 4-in. leaves with bluish undersides. Catkins of male plants are main drawsoft, silky, pearl gray, to 112 in. long.
S. gracilistyla. ROSE-GOLD PUSSY WILLOW. Shrub. Zones US, MS; USDA 6-7. To 610 ft. tall, 12 ft. wide. Narrowly oval, 2- to 4-in.-long leaves are gray-green above, bluish green beneath. Male plants produce plump, gray, furry, 112-in.-long catkins with numerous stamens sporting rose-and-gold anthers. Cut branches for arrangements to curb plant's size. Every three or four years, cut plant back to short stubs; you'll get very vigorous shoots with large catkins. 'Melanostachys' has black catkins with red anthers.
S. matsudana (S. babylonica pekinensis). HANKOW WILLOW. Tree. Upright, pyramidal growth to 4050 ft. tall, 3040 ft. wide. Bright green, narrow, 2- to 4-in.-long leaves. Can thrive on less water than most willows.
'Navajo'. GLOBE NAVAJO WILLOW. Large, spreading, round-topped tree to 70 ft. tall and wide.
'Tortuosa'. CORKSCREW WILLOW. To 30 ft. tall, 20 ft. wide; branches fantastically twisted into upright, spiraling patterns. Valued for winter silhouette and cut branches for arrangements.
'Umbraculifera'. GLOBE WILLOW. To 35 ft. high and wide. Umbrella-shaped crown with upright branches, drooping branchlets.
S.nigra. BLACK WILLOW. Tree. Zones US, MS, LS, CS; USDA 6-9. Native to central and eastern North America, where it is common along streamsides and riverbanks. To 3060 ft. tall, 30 ft. wide. Narrow, finely toothed leaves to 7 in. long are shiny dark green above, light green beneath. Tree bark is scaly, furrowed, and dark brown to black. The soft wood is used for making baskets and wicker furniture. Tolerates flooding; often used for wetland reclamation. Will take full sun but does best in partial shade.