A weeping willow loses its leaves during the fall in order to survive harsh winter weather conditions. The olive-green leaves turn to yellow during the fall, and the tree drops the leaves before winter arrives.
Deciduous trees, such as weeping willows, lose their leaves seasonally. The verdant leaves of the weeping willow require a large amount of water to maintain, and enough water is not available during winter. Just before winter, the tree breaks down the organic compounds from the leaves and reabsorbs the nutrients from them, which are reused when spring comes. When a weeping willow tree drops its branches or leaves off-season, this may indicate that the tree is deficient from nutrients. It must be irrigated immediately to prevent the tree from dying.