Plants need water and nutrients to grow; nutrients that are naturally found in most soils. The concentration of such nutrients can vary, however, so most gardeners choose to give nature a boost by adding nutrients to the soil in the form of fertilizer. Fertilizers can vary in their components. The highest quality fertilizers will have more nutrients included in their mixture and less fillers. Fertilizers can be either completely natural (organic) or chemical.
The primary ingredients in most fertilizers are the most important nutrients plants need to grow. These nutrients are nitrogen, phosphorus and potassium. The amount, or percentage of each nutrient as contained in the fertilizer is indicated by the bold numbers on the front of the bag. A bag labeled 10-10-10, for example, has equal amounts of each nutrient. Nitrogen, represented by the first number in the three-number sequence, is essential for foliage development and the lush, green color so desired in lawns. Phosphorus, the second number, is necessary for root growth and is especially important when establishing new plants. Potassium, represented by the last number, promotes blooming and fruiting.
Most fertilizer blends also have secondary nutrients. These are also necessary for plant growth. Calcium helps plants make salicylic acid, which helps the plant respond to and defend against external threats. Magnesium, another secondary nutrient, is an essential part of the process of photosynthesis.
Micronutritrients are included in the ingredients of higher quality fertilizers. These might include minerals such as copper, iron, zinc, chlorine, boron, manganese and nickel. The benefits of micronutrients vary, but they range from aiding in chlorophyll formation (iron) to preventing the growth of some types of fungi (copper).
Fillers are also a component of fertilizers. They are meant to aid in the distribution of the minerals. Limestone and sand are common fillers. Some fertilizers have more fillers than others. To determine the amount of filler in a bag, add together the percentage of macronutrients, then divide the weight of the bag by that number. Subtract the answer from the weight of the bag. For example, a 50 pound bag containing nutrients of 10-10-10 (50 times .30) contains 15 pounds of nutrients and 35 pounds of filler.