This study describes biomass production, colony formation, and clonal spread via root stems of a wide-ranging North American willow species, Salix interior (INT), one of the few willows that can produce colonies of hundreds of upright stems arising from a shallow horizontal root network. Eight INT clones were tested in a common-garden experiment on two distinct site types (shale rock overburden and coarse gravel erosion sediments) with very low nitrogen and nutrients on a former coal mine site. Survival, height growth, aboveground biomass, and number of root stems were quantified following 3 years of growth after establishment as rootless stem cuttings. Clonal differences were significant for survival and height. There was a significant positive relationship between height growth and survival, both of which are indicators of plant vigor. On coarse gravel outwash, the more vigorous clones for height growth also produced more root stems. Loose sand and gravel outwash deposits promoted a more rapid spreading of the shallow horizontal root network than the less penetrable shale rock overburden that dominates this former coal mine site. Colony-forming willows such as INT may eliminate the need for periodic plantation re-establishment, providing a major cost advantage over conventional short-rotation, coppice-based woody biomass plantations. Also, this species is a natural invader of oil sands tailings in northern Alberta and provides one of our best prospects for rapid re-vegetation of these mine tailings for eventual forest restoration.