Lawn care requires a lot of work, including proper fertilization practice. Grass uses up nutrients in the soil it is growing in. If nutrients are not replaced at a greater rate than the rate at which they are used, a deficiency occurs, reducing grass health and causing aesthetic problems.
Plants require three main elements: nitrogen (N), phosphorous (P) and potassium (K). These three elements are required in the lawn in greater amounts than other elements in the soil. Micronutrients are also required in smaller amounts. Air and water provide some, and these are often not included in synthetic lawn fertilizer.
Unfertilized lawns are more prone to disease than lawns that are properly fertilized, according to the Oregon State University Extension. Red thread, rust and root diseases are common in unfertilized lawns. Lawns that are thin and weak are susceptible to disease. The application of fertilizer strengthens the grass, keeping disease at bay.
Fertilizers improves the growth of the grass. Nitrogen increases the growth of the roots, which improves water uptake and makes the grass look greener. With too little nitrogen from fertilizer, plants yellow and thin. Too much nitrogen causes shoot and leaf growth that weakens the plant. Phosphorous improves the development of root growth. Phosphorous is not needed in lawns that already have a large deposit of phosphorous. Potassium reduces the chance of disease.
Fertilizer is applied by every 1,000 square feet or acre. Different lawns require higher or lower maintenance according to the grass variety. High maintenance lawns include Kentucky bluegrass and perennial ryegrass varieties. High maintenance lawns require 3 to 4 pounds of nitrogen per 1,000 square feet per year. Low maintenance lawns only require 1 to 2 pounds of nitrogen per 1,000 square feet per year.
Application timing effects the health of the lawn. Fertilizing at the wrong times of the year causes overgrowth or burning of the leaf blades. Traditionally, fertilizers are applied in the late summer and fall, according to the University of Minnesota. Another application in October or early November improves the health of the lawn over the winter.