Pollination -Pollination: Narrowleaf willow is primarily insect pollinated

Seed Production and Dissemination - Seed production: Narrowleaf willow produces many small seeds with morphological adaptations to enhance dispersal. Flowering and seed production may begin as early as age 2 to 3 years. In general, willow seeds are dispersed primarily via wind and water. Narrowleaf willow seeds are small, fragile, light, and sufficiently aerodynamic to be wind-dispersed. Narrowleaf willow seeds are nondormant and quickly become desiccated if not on a moist substrate. Seed viability beyond 1 week is rare, and viability lasts no longer than 3 weeks.

Seedling Development - Seedling recruitment of narrowleaf willow may be limited by site availability - establishment requires areas that are both close enough to streams for adequate water and yet protected from intense scouring during floods. Seedling mortality also results from herbivory, pathogens, and competition with other seedlings for available resources. Narrowleaf willow seedlings have been characterized as "fast growing". Annual height increases are 12 inches (30 cm), and stem diameter increases at 0.1 inch (2.6 mm). Shoot growth in willow species varies from year to year in response to resource accumulation from the previous year. Snow cover, early season temperatures, and drought may have little visible effect on current year's growth but may reduce shoot growth and rooting success the following year. Willow height growth is most rapid during late afternoon and early evening.

Asexual regeneration- Narrowleaf willow typically develops dense clonal thickets from root sprouts. Stems develop from shoot buds on lateral roots and form extensive spreading colonies. This colonial habit allows narrowleaf willow to dominate riparian sites. Individual narrowleaf willow plants are generally shrub-like, though older individuals may resemble small trees. Clones expand vegetatively along moisture gradients resulting in dispersed and linear clones, with new clones developing progressively closer to moisture sources. Due to potentially high seedling mortality, asexual clones may be largely responsible for narrowleaf willow's success. Because narrowleaf willow reproduces primarily through asexual sprouting, lack of a resident population can limit establishment of narrowleaf willow, even on favorable sites