Potassium (K), the last number of the N-P-K fertilizer analysis, is a vital “vitamin” for the grass that helps it ward-off diseases during cold, harsh winters. Accordingly, when grasses are deficient in potassium, they are susceptible to temperature changes. Potassium also helps lawns absorb more nutrients in the soil. The grass uses potassium to effectively make proteins and starches to store for the winter.
as your last fall fertilization of the season.
high-K formulation (10-0-20) is ideal for the lawn as the winter approaches. Some competitive fall fertilizers have high amounts of nitrogen in them. Too much nitrogen applied in the fall encourages lawns to keep growing into the winter, a time where it should be dormant. This excessive “winter” growth will foster spring diseases, like red thread and snow mold.