Willows are a very large and diverse group of trees. More than 100 species grow in the United States and Canada, ranging in size from a few inches tall to trees as large as 4 feet in diameter. Six species reach tree size in Iowa; they are the Missouri, pussy, sandbar, shining, peachleaf, and black willows. Black willow (Salix nigra) is the largest of the tree willows in Iowa, attaining heights of 30 to 60 feet and a diameter of 14 to 24 inches. It is native to all of Iowa except the far northwest corner.
Habitat: Found growing along streams, lakes, and bottomland woods. Grows in most of the state.
Hardiness: Zones 2 though 8
Growth Rate: Extremely fast (3 to 4 feet per year over a 20 year period).
Mature Shape: Large, low branching tree with long branches and flexible stems that form a broad, open, round-topped crown.
Height: 75 to 100 feet
Width: 50 to 100 feet
Site Requirements: Prefers moist soils and are frequently found along ponds and streams. Needs full sun.
Leaves: Alternate, simple, long, and thin.
Flowering Dates: February - June
Seed Dispersal Dates: April - May
Seed Bearing Age: 10 years; optimum seed production 25 to 75 years
Seed Bearing Frequency: Yearly
Seed Stratification: Seeds disperse in the spring and immediately germinate. No stratification period is needed.
It is common along streams, lakes, or wet areas; it requires moisture to survive and grow. It often grows as leaning, multiple stem trees, although it can develop with single stems when growing under forested conditions. Its common associates in the floodplain woodlands include cottonwood, green ash, silver maple, boxelder, river birch, and other moisture loving trees.
The alternate simple leaves are narrow and taper pointed, with long, sharp curved tips and finely toothed margins. They are shiny light green above, and duller green below; the other tree willows in Iowa will be blue-green or white on the lower surface. The twigs are very slender, yellowish brown to red and very brittle at the base. The buds are reddish brown, ovoid, and less than 1/4 inch long. The terminal bud is absent. The bark on older trees is dark brown to black and deeply furrowed. Male and female flowers occur on separate trees. The fruit is a capsule containing many tiny, silky-haired seeds.
Black willow was once planted extensively in farmstead groves and shelterbelts because of its fast growth. It is not used very much today because of its relatively short life. It can be used in riparian plantings along waterways to stabilize and protect riparian zones. It is not typically used for shade or ornamental purposes.
It is the only willow which is large enough to provide wood products. The wood is soft, light in weight, smooth textured and nondurable. It is used for rustic furniture, polo balls, boxes, crates, construction lumber, paper pulp, charcoal and firewood.