Some favor natural fertilizers, using them to complement organic gardening practices. Others prefer the convenience of chemical products in controlled-release form. Applied properly, both have their appropriate uses in the garden. These fertilizers include all kinds of animal manures, fish emulsion, and meals made from blood, bone, alfalfa, cottonseed, kelp, and soybeans. These products are usually more expensive, pound for pound, than chemical fertilizers.
Most natural fertilizers contain lower levels of nutrients than chemical products.
However, since they depend on soil organisms to break down the nutrients, they're not as effective in chilly weather, when such organisms are less active. On the other hand, the insoluble nitrogen they supply tends to stay put in the soil and not move into the water supply, where it could have harmful effects. Natural fertilizers also improve the texture of the soil and increase the amount of beneficial microorganisms. For best long-term results, dig them into the soil early in the season. They usually have higher levels of nutrients and a larger percentage of soluble nitrogen than natural fertilizers.