Garden soil will turn black and rich in organic matter and fertility. Leaves kept in bags until spring can be spread and tilled in then, just before seed is sown. Seedlings won't grow well if the dirt is overloaded with unrotted leaves. Empty the bags, let leaves rot for 9 months. Weed seeds will be denied the light they need to sprout if you hoe or cultivate first, then mulch row middles with rotted leaves after plants are growing well.
Maple leaves rot faster than oak leaves.
Thin green nitrogen-rich maple leaves, which fall to the ground in early autumn, will rot quickly. Thicker oak leaves fall later and rot more slowly. Scientists have found that fallen maple and oak leaves release natural phenols during the first 6 to 8 months of the rotting period. These phenols inhibit growth of seedling roots, but rot and disappear from soil and mulch within 9 months of weathering. Better to keep dead leaves and leaf compost out of an area where seeds will be sprouting until after plants are up and growing well.