Potassium (K) is the third major nutrient listed on fertilizer bags, following nitrogen (N) and phosphorus (P). Often overlooked, potassium plays an important role in maintaining turfgrass health and overall plant resilience. It is vital for preparing a lawn to withstand various environmental stresses. Understanding where to find the right potassium source and how to apply it correctly leads to a stronger, more vigorous lawn.
The Role of Potassium in Lawn Health
Potassium regulates internal processes within the grass plant. As an ion, it helps manage the opening and closing of stomata, the tiny pores responsible for gas exchange and water transpiration. Adequate potassium levels allow the grass to better control water loss, significantly boosting its tolerance to drought and heat stress. This element also strengthens the plant’s physical structure by enhancing cell wall strength, which improves the turf’s resistance to common fungal diseases like brown patch and dollar spot. Furthermore, potassium nutrition supports deep, robust root development and increases the plant’s ability to withstand cold temperatures.
Identifying the Right Potassium Source
The three numbers listed on fertilizer bags represent the NPK ratio, with the third number indicating the percentage of potash (\(K_2O\)). For instance, a bag labeled 10-10-20 contains 20% potash by weight. To correct a soil deficiency, look for products with a high third number and a low or zero second number (e.g., 0-0-50 or 7-0-20) to avoid adding unnecessary phosphorus.
The two most common chemical forms are Muriate of Potash (MOP), or potassium chloride (KCl), and Sulfate of Potash (SOP), or potassium sulfate (\(K_2SO_4\)). MOP is generally more affordable and contains a higher concentration of potassium (around 60-62% \(K_2O\)). However, MOP has a higher salt index due to the chloride content, which can increase soil salinity and potentially cause burn damage if over-applied.
SOP is the preferred option for lawns because it has a lower salt index, reducing the risk of turf burn and soil salinity buildup. Sulfate of Potash also provides the added benefit of sulfur, a nutrient that supports chlorophyll formation and protein production. While SOP contains a slightly lower potassium concentration (around 50% \(K_2O\)) and is more expensive, the reduced risk of negative effects makes it a better choice for turfgrass.
Retail and Wholesale Options for Purchasing
The choice of vendor determines the concentration and form of potassium available.
Large chain retailers and big box stores primarily stock all-purpose NPK blends. These blends usually contain a small amount of potassium, suited for maintenance rather than correcting a significant deficiency. These locations offer convenience for common lawn fertilizers.
For products specifically designed to boost potassium levels, local garden centers and nurseries are a better source. They often carry specialized blends like “winterizer” formulas with a higher K ratio and can provide tailored advice for local turf species.
The highest concentration potassium sources, such as pure Muriate of Potash (0-0-60) or Sulfate of Potash (0-0-50), are most reliably found at agricultural suppliers or farm co-ops. These vendors cater to commercial growers, offering bulk purchasing options and materials with the highest nutrient percentages. Landscape supply houses also carry concentrated materials, often including liquid forms like potassium thiosulfate. Online vendors specialize in shipping concentrated products, which is useful when local sources are limited, but shipping costs should be considered.
Safe and Effective Application Methods
The most important step before applying potassium is to conduct a soil test. This test provides an accurate measurement of existing nutrient levels and soil pH. Applying potassium when it is not needed can lead to a nutrient imbalance, potentially inhibiting the grass’s ability to absorb other nutrients like magnesium and calcium. The soil test report specifies the exact amount of potash, measured in pounds per 1,000 square feet, required to reach an optimal level.
The best time to apply potassium is in the fall or before anticipated stress periods, such as summer drought or winter dormancy, allowing the plant to build up reserves. Granular potassium should be spread using a rotary or drop spreader to ensure a uniform application across the lawn surface. To prevent “striping” or uneven feeding, walk at a consistent pace and slightly overlap the passes.
After spreading the granular fertilizer, water the lawn thoroughly. This dissolves the particles and moves the potassium into the soil, minimizing the risk of leaf burn, especially with higher-salt index products. Always follow the specific application rates recommended by the soil test and the product label to ensure the grass receives the correct amount.