From the Sierra Club:
Cooler temperatures bring fallen leaves, and fallen leaves offer the chance to create nutrient-rich soil that will eventually help your spring garden bloom. Instead of cramming raked leaves into plastic bags that end up in landfills, use them to begin a compost pile. Decaying leaves are high in carbon, and will provide your pile’s essential brown material. Need some greens for the nitrogen? Add food waste (apple cores, pumpkin rinds, and so on) begotten from that pick-your-own adventure.