Plant food, most commonly referred to as fertilizer, is necessary for all plants to grow. In nature, this food is provided by the natural process of decomposition that all organic materials undergo. Their nutrients are returned to the soil, where they are in turn absorbed by plants. In gardens and yards, gardeners often apply both organic and manufactured fertilizers instead.
Macronutrients are the most important part of fertilizer, and often the first thing gardeners notice when looking at plant food packages. Nitrogen, phosphorus and potassium comprise the three macronutrients. They are often referred to as NPK levels, and are expressed on fertilizer packaging by numbers, in that order. These numbers represent the percentage of each nutrient that is present in the package. A fertilizer package marked 10-10-10 has 10 percent each of nitrogen, phosphorus and potassium.
Micronutrients are the other nutrients that plants need to grow, but that are not needed in such great amounts. They include molybdenum, copper, zinc, iron, boron, magnesium, manganese, sulfur and calcium. The amounts present are usually not indicated on the front of a fertilizer package. Instead, they are indicated on the back or side, like nutrition information on food.
Organic fertilizers come from organic sources, usually animal or plant-based. These include compost, manure, bone and blood meal, and fish and seaweed emulsions. All of these are slow-release in comparison to conventional fertilizers because the nutrients in them must be broken down within the soil before plants can absorb them. They are more popular with home gardeners than commercial gardeners due to their comparatively high price, according to the Michigan State University Extension.
Conventional fertilizers are chemicals that are manufactured. Many are absorbed more quickly by the soil, although slow-release conventional fertilizers are also available. Due to their quick absorption, gardeners must take special care to only apply manufacturer-recommended amounts when feeding plants. Overapplication can cause tender plant growth to be burned by the sudden rush of chemicals.
Different plants require different fertilizers to grow healthy and vigorous. Take care to choose the fertilizers best suited to whichever plants you are growing. You should also be aware that fertilization is an ongoing process. Both organic and conventional fertilizers have recommended application rates printed on their packaging. Very heavy feeders, such as tomatoes and cucumbers, will require more frequent fertilization than some other plants.