Compost is a wonderful thing! Just as they name suggests, this product is composted leaf and limb material. It's dark, humus-rich, and ground to a uniform consistency. Compost is great for amending planting mixes. Use as much as a 50% compost and 50% super soil blend for garden applications. It's available in bulk or in 1 cubic foot bags.
(Just for fun, roll around in the compost pile a bit, be sure to get covered well with compost dust, then brag about how hard you've been working in the garden!)