Organic fertilizers are the products of natural decomposition and are easy for plants to digest. Made from natural sources, organic fertilizers provide garden plants with slow-release, consistent nourishment. Such a “health food" diet makes your plants strong and self-sustaining. Rather than depend on you for feeding them a steady supply of synthetic fertilizers, they find what they need in soil that has been fed with organic fertilizer. Organic fertilizers that feed the soil and sustain plants include animal waste and byproducts, such as bird and bat guano, blood meal, bone meal and feather meal, as well as fish and kelp fertilizers.