Willow species along Putah Creek can be notoriously difficult to identify due to their similar characteristics and what appears to be very minute differences to the untrained eye. Sandbar willow (salix exigua) might be an exception with its almost silvery green appearance and its shrubby growth. Sandbar willow can be distinguished from the other native willow species in this region through its leaves and overall color. This species of willow has leaves that are ¼- ½ inch in width and up to 5 inches in length as opposed to much wider leaves of Goodings and Red willow (Goodings willow is green in appearance with the same shade top and bottom of the leaf whereas Red willow has a different shade of green on the underside of its leaves). Another giveaway for the sandbar willow its entire leaf margins with occasional, irregular, and widely spaced teeth.
Sandbar willow is a medium sized deciduous shrub that can grow in thickets and be up to 16 feet tall. The denseness of its growth makes it great cover for wildlife.This willow enjoys wet conditions and can even withstand severe flooding, but does not tolerate drought well. Because of its love for water, sandbar willow does best in deep, moist loamy soils like the banksides of a streambed. The plant’s propensity for forming thickets comes from its ability to clonally reproduce by roots or “suckers”.
Sandbar willow is dioecious meaning the pistallate (female) and staminate (male) flowers are on separate plants. The plant flowers in early spring after the leaves appear and creates catkins with male catkins slightly longer than those of the female. Their flowers are yellow or white in appearance. Sandbar willows do produce fruits that appear as a cluster of capsules with small, shiny, white, silky seed inside. Their seed, however, is only viable for a limited period of time, at most a couple of days. Well adapted to flooding disturbance, sandbar willow can easily resprout from its stems. Instead of seed, sandbar willow can be propagated best through “cuttings” or “poles” where a section of a branch is placed directly in soil to resprout.
Because of its tendency to resprout through its basal roots, sandbar willows can take over and occupy an open space with direct sunlight with ease. This makes it an ideal candidate for streambank stabilization, but it's known for being aggressive and sometimes invasive. Sandbar willow thrives in full sun locations and loves to keep its “feet” wet along the streambank. Sandbar willows are great pollinator plants and are known to host a variety of butterflies and moths including Western Tiger Swallowtail, Mourning Cloak, and Lourquin’s Admiral as well as some gall forming wasps.