The Effects of Potassium on a Lawn

Role of Potassium

• Potassium, as one of three macronutrients that plants require for health, is very important to lawn grasses. Potassium plays an essential role in plant growth, helping in cell wall development. It also regulates several physiological processes including the efficient use of nitrogen and water movement within the plant. Adequate potassium improves a lawn's wear and drought tolerance and protects vegetation from lawn diseases like red thread.

Symptoms of Potassium Deficiency

• A potassium deficiency in a lawn is difficult to recognize and may not be diagnosable without a soil test. because potassium helps grass resist disease and tolerate wear and environmental conditions, suspect a deficiency if turfgrass becomes affected by disease and loses vigor or turns yellow. Other possible general symptoms include drooping, yellowing that begins between veins before spreading and low drought and wear tolerance. Excessive potassium can interfere with calcium and magnesium absorption by plants.

Fertilizer Recommendations

• The best way to determine a suitable potassium application rate for a lawn is to have a soil test conducted. If a soil test is not conducted, however, the Purdue University Turfgrass Science Program provides some general recommendations. Determine the best application rate for nitrogen for the lawn, then apply one-half as much potassium as nitrogen and one-fourth as much phosphorus as nitrogen. Make a heavy application in fall and a light application in spring. Sandy soils are less able to hold potassium than other soil types and generally require more fertilizer. Potassium can be applied as a stand-alone fertilizer outside of a complete fertilizer as potash. Other sources of potassium include seaweed, greensand, wood ashes and sulfate of potassium, or muriate.

Other Primary Macronutrients

• The other two primary macronutrients that must be taken into account alongside potassium when testing soil or fertilizing a lawn include nitrogen and phosphorus. Nitrogen promotes strong, vigorous growth and too little available nitrogen will stunt growth and give turf a yellowish cast, while excessive nitrogen can cause rapid, weak growth. Phosphorus is important for early vigor and root growth. Inadequate phosphorus gives grass blades a reddish or purplish-gray cast. Excessive phosphorus can interfere with a plant's ability to take up other nutrients.