Legend has it that Alexander the Great's doom was sealed when a weeping willow branch brushed his crown from his head as he crossed the Euphrates; the event signaled his rapid demise to ancient Babylonian soothsayers who associated the tree with death, sorrow and tears. Modern gardeners are more likely to think of romance and fleeting beauty when they admire the willow (Salix babylonica), since the tree loses its long, glorious tresses every autumn.
The weeping willow is an imposing tree, growing up to 70 feet high with a 70-foot spread. It is a backyard tree appropriate only for those with large grounds. Although the willow produces yellow flowers in springtime, the leaves are the main show. They grow simple and lance-shaped, up to 8 inches long and 4 inches wide. A tender green when they appear in early spring, they quickly mature to dark green and then blaze yellow in autumn just before falling.
Annual Growth Cycle
The willow is deciduous and never retains its leaves over winter. It is among the first trees to leaf in the spring. New growth appears in March or April in most areas, giving the bare branches a green hue. The leaves grow in quickly, covering the tree in a matter of weeks, and new growth approaches 36 inches a year until the tree attains its mature size. In the fall, the willow leaves turn yellow but remain on the tree long after many other leaves have fallen. Winter brings a season of dormancy where the tree ceases growing and remains inactive.
To irrigate all this foliage, willow roots aggressively seek water in the underlying soil, spreading three times as far as the tree's drip line in all directions. The roots remain fairly close to the surface but can easily become invasive. Think twice before planting a weeping willow near your sewer or water lines, since its roots are strong enough to break through pipes and lift sidewalks. Many willows are planted near ponds and rivers to provide the thirsty roots with adequate irrigation. However, uncontrolled willows propagate quickly near streams and their roots and detritus can overwhelm a waterway.
Willows need sunlight. They prefer full sun but tolerate partial sun, and they are soil tolerant; the trees grow in clay, loam or sandy soil with a pH ranging from highly acidic to highly alkaline, as long as they get sufficient water. If you have wet, alkaline soil and live in U.S. Department of Agriculture plant hardiness zones 6 though 9, this may be the tree for you. Cultivars exist that offer exotic leaves, but each grows best in a specific hardiness range. The cultivar "Aurea" (Salix babylonica "Aurea") offers golden-green leaves in USDA zones 6 though 8, while "Crispa" (Salix babylonica "Crispa"), with leaves that curl like rams' horns, thrives in USDA zone 6.