Every autumn, residents across Seattle give away a valuable resource that could be helping their gardens. They rake and bag their fallen leaves, hauling paper sacks and plastic yard waste containers full of them to the curb for weekly removal. Clever gardeners know those leaves could be put to work, enriching soil and mulching garden beds.

An easy beginner method of using your fallen leaves is to simply mound them up over garden beds being readied for winter for use as a mulch. The leaves will break down and prevent loss of soil from heavy winter rains. They will also insulate and protect plants from frost. Your soil will benefit from the protection the leaves provide,and the organic matter returned via their decomposition.

Dried autumn leaves provide the essential carbon (often referred to as the “brown”) needed for composting. When added to an equal amount of “green” material, such as grass clippings, they make a perfect balance to create rich, dark compost that bolsters soil fertility. Yet both untreated leaves and grass are often set out for yard waste pickup,when they could be serving a purpose in the garden.

For dedicated soil builders, these organic materials are highly sought after items. I know one woman who shows up on her neighbor’s doorstep each autumn, rake in hand, and offers free leaf removal if she can keep the leaves for use in her garden. Other gardeners have been known to help themselves to bags of raked leaves or collected grass clippings that others have put out for pickup.

Making a batch of leaf mold is another way to use seasonal resources. To do this, collect leaves in a round yard waste composter or a cylindrical wire cage made from a length of fencing and leave them to sit until broken down. Some people run their leaves through a chipper or go over them with a lawnmower to cut the leaves into smaller pieces, others simply use the leaves whole. The trick is making sure the pile doesn’t dry out. By springthe leaves will have broken down and can be worked into your garden beds. Experiments at Seattle’s Interbay P-Patch showed increases in soil fertility after they began adding leaf mold to the soil.

If you have plants, trees or shrubs that were diseased this year, it’s best to send those leaves to the municipal composting system so you don’t spread the disease.

However you use them, consider keeping your leaves this year. Why give up such a valuable resource? Fallen leaves are natural, useful and free—and an important part of soil building.