Keeping trees trimmed is important throughout the year, but to ensure that they stay healthy and attractive during the fall and winter season, trimming trees is critical. Just as it does in the summer, trimming helps to give fallen leaves a chance to decompose and minimize 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).