Although most gardens need similar fertilizer components, different types of gardens need different rations of the three main components of fertilizer: Nitrogen, phosphorus, and potassium. Most fertilizers list the percentage of these ingredients as an N-P-K number. An N-P-K number might be 20-10-10 for a high nitrogen fertilizer. That number indicates that the fertilizer is 20 percent nitrogen, 10 percent phosphorous, and 10 percent potassium. A 10-10-10 fertilizer has 10 percent of each nutrient. When fertilizing your garden, you will need to consider what types of plants are growing and their basic fertilization needs. Some powdered fertilizers need to be watered in after application, others should not be applied before a rain. Follow all package directions when fertilizing.
Nitrogen in fertilizers is used primarily for green plant growth. Lawn fertilizers, for example, are higher in nitrogen to help encourage green growth. Fertilizers high in nitrogen are also good for green leafy vegetables like lettuce or spinach. However, for flowers or vegetables that grow from flowers, like peppers, cucumbers, and tomatoes, high nitrogen fertilizers can cause rapid vegetative growth that uses energy that is best used by flowering and vegetable production. Using high nitrogen fertilizers on flowers and some types of vegetables can reduce production. Most organic fertilizers won't supply too much nitrogen. However, chemical fertilizers, such as urea and ammonia based fertilizers, can cause a spike in soil nitrogen.
Phosphorus is used by plants in photosynthesis. It helps to create strong stems and sturdy growth. Plants that have too little phosphorus can look spindly. Plants that are deficient in phosphorus don't produce as many flowers, seeds, and flower-based vegetables. Adding phosphorus to your flower and vegetables can help improve flowering. Most balanced fertilizers have adequate phosphorus. Phosphorus is fixed in organic matter, so ensuring adequate organics in your garden soil will help your plants use available phosphorus. Phosphorus is available in most organic fertilizers and has been synthesized for use in chemical fertilizers. Chemical sources of phosphorus in fertilizers include, among others, diammonium phosphate, monoammonium phosphate, and triple superphosphate.
Like phosphorus, potassium is important for efficient plant photosynthesis. Potassium is important in plant growth, especially in root growth. Gardens that are deficient in potassium can have weak root structures and can have problems regulating water. Plants suffering from a potassium deficiency can suffer from pest problems. Many organic fertilizers naturally have potassium. Chemical sources of potassium include potassium chloride, potassium sulfate, and potassium nitrate.