Salix boothii is a medium-sized tree, with yellowish or reddish branches, sometimes lightly hairy, and light green, smooth-edged leaves, between three and four times as long as wide. Leaf bases are rounded, or sometimes projecting downwards either side of the stalk. Leaf margins may be slightly wavy. Either surface of the leaves may be glabrous or sparsely hairy.
The inflorescences are short, narrow, spikes - catkins - which contain either stamens (which have thin white filaments and small yellow anthers), or light green pistils. The catkins are up to 3 inches long, and hang downwards. The fruits are light green capsules, up to a third of an inch long, arranged in a dense spike; the open to reveal a mass of fluffy seeds.