Similarly, fertilizing in late spring or summer will pull food reserves away from the roots and encourage summer stress. Briefly, N promotes growth and gives turf a healthy color. Without sufficient N, growth slows or stops, and the lawn becomes yellowish. Too much N can overstimulate shoot growth at the expense of good root growth, or may be flushed from the soil because it is highly mobile. When the root system is compromised, the turf becomes less drought and stress resistant.
P is essential to produce strong root growth.
It is particularly important for root development of new plantings. It is not readily flushed from the soil by watering and is either needed in smaller quantities or not need at all, depending on soil test results. K is needed for overall hardiness and stress resistance in the turf. So for either P or K, a soil test is the best way to determine how much, if any, nutrient is needed and should be performed before fall turfgrass establishment and maintenance. This site features basic information on sod production and an 800 number for additional questions.