Compost.
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Compost is an organic, nutrient-rich food for plants that can be harvested yourself; it's the eco-answer to fertilizer. Place anything from wood ash, dead leaves, and shrubbery clippings (brown matter) to vegetable, fruit, and coffee waste (green matter) in an old metal trash can with holes in the top. The rule of thumb is half brown, half green. With occasional turning, it will become a rich black fertilizer to be scattered over your lawn as often as you can produce it.