Fertilizing
Fertilizing Not all soils have enough nutrients or the right balance of nutrients. In addition, plants remove nutrients from the soil as they grow, so these nutrients must be replaced in order for the soil to remain productive. For these reasons, gardeners enhance soil by adding fertilizer , a material that contains one or more of the nutrients plants need. Fertilizers are divided into two categories: synthetic and organic. Synthetic fertilizers are concentrated salts or minerals, some of which are produced as by-products of petroleum production. Organic fertilizers originate in plants, animals, or minerals and include compost, seaweed, and ground bone. (For advantages and disadvantages of synthetic and organic fertilizers, see Organic Farming .) Fertilizers usually are sold in packages, on which the percentage by weight of the macronutrients nitrogen (N), phosphorus (P), and potassium (K) are listed on the label—always in the order N-P-K. For example, a fertilizer that is labeled 10-5