It is important to keep trees trimmed throughout the year. However, it is crucial to trim trees in the fall and winter to ensure they remain attractive and healthy. As it does in summer, trimming leaves gives fallen leaves a chance for decomposition and reduces the risk of disease-causing pests. As we prepare for winter, trimming gives our trees a clean look. Trimming is best done in the early fall, when there is less risk of frost damage to young growths (new shoots).