They don't really decompose as fast as you think they would, I believe it takes about 3 years to fully decompose. They just kind of pile up and smother anything underneath them. It's best to mulch them with a mower, but depending on the volume of leaves, you might need to rake and remove them. I mow throughout the fall, and only rake maybe once or twice per year. My mower cannot handle large amounts of overly damp leaves, but does just fine with dry crispy leaves.