Hybrid willow trees have an expansive root system that sends up suckers (new growths that will eventually form into another tree). Avoid planting your willows near homes, buildings, and sewer lines, as their roots can cause serious damage. While they are not quite considered invasive, the trees will spread around your property if not controlled. Remove suckers as soon as you see them forming around the base of a tree, as they will “suck” valuable energy from the tree that could be spent in more productive ways.