Natural fertilizer is not a new concept. Ancient forests fed on the decomposing plants that covered their floor, and native peoples nourished their croplands with dead fish and bird guano. Today's gardeners use organic fertilizers to enrich their lawn and garden soil without the use of expensive and potent chemical fertilizers. All you need to feed next year's lawn may be growing right in your yard this year.
Natural fertilizers use organic sources of nutrients necessary for plant growth. Well-rotted plant and animal remains contain nitrogen, phosphorus, phosphates and other elements that can stimulate the growth of lawn grasses.
The terms "natural" and "organic" are often used interchangeably; no official criteria exist for either term. Natural preparations containing bone meal, a source of phosphates often contain rock phosphate, a mined material (not a chemical compound) upon which organic experts would frown.
Organic compost heaps must balance nitrogen-rich and carbon-rich plant-based materials but many natural heaps are regulated using "biostimulants", preparations designed to control the rate of decomposition.
The Right Manure
Manures stack up differently depending on species diet. The emphasis on organic gardening--and manure's sizable content of nitrogen and other nutrients like iron--have encouraged development of processes to make it safe to use and relatively odorless. That said, any manure should be composted and "well-rotted" before use. Chicken manure is relatively low in nitrogen but high in phosphates. Steer, horse and sheep manure are high-nitrogen sources and sheep manure has a high proportion of potassium.
Manure from meat-eating animals like dogs and cats should never be used because it may contain bacteria and viruses that will attack plants. Bat guano and sanitary treatment sludge have been used for years to provide a high proportion of nitrogen that releases slowly throughout the season. Humans, of course, are meat-eaters; after early problems, the sludge marketed as Milorganite has treatment for harmful microbes built into the manufacturing process.
Additives and Conditioners
A variety of natural materials can be used in the fall or when new lawns are seeded to provide slow-release nutrients for strong roots and crown growth. Organic materials like fish oil and bone meal provide moderate nutrients over a long period of time. Well-rotted compost and fish oil provide nitrogen (although the fish oil can be smelly), bone meal provides phosphates and hardwood ash or potassium sulfate provides potassium. The right balance, unlike commercial fertilizers, must be determined by the lawn-owner.
A soil test by a state university agricultural extension can give guidance as to the proportion of each nutrient needed. Compost lightens heavy soil as well as providing some light feeding.
Top Dressing and Maintenance
Most lawn-owners know that leaving grass clippings on the lawn provides a source of natural nitrogen. It also conserves nutrients pushing at the top of the blade to make it grow. Top dressing with manure or a mixture of compost and humus in the fall can also be beneficial, giving roots a constant drip of nutrients over the winter for a fast green-up in spring.