Although nitrogen is the most important nutrient for a healthy lawn, potassium and phosphorus play a role, as well. Potassium is an essential nutrient for strong root formation and plant health. Conduct a soil test, first, though, to accurately determine what nutrients your lawn needs. Too much fertilizer can damage lawns and pollute ground water.
Potassium encourages winter hardiness, especially in warm-season grasses that enter dormancy in late fall in warm climates. Potassium encourages good water uptake and strong cell and root formation that helps grass survive winter temperatures.
Because potassium builds strong cells and roots, it helps grass plants fend off disease and metabolize food more efficiently. In conjunction with nitrogen and phosphorus, it can produce a strong, disease-free lawn.
Potassium is often present in the soil, but may be in a form that is unavailable to plants. Signs of potassium deficiency include burned grass blades when the lawn is receiving sufficient moisture or weak roots and stems. Grass plants deficient in potassium may be more affected by drought, insect pests and disease.
Winterize grasses in the fall with a high-potassium fertilizer, such as potash, potassium sulfate or muriate of potash. Avoid fertilizers high in nitrogen late in the season or apply them after the first frost when the grass is dormant. Winterizing fertilizers, high in potassium, can be applied in the spring, as well, to encourage disease resistance and hardiness.