Applying fertilizer to your lawn during the summer months differs significantly from spring or fall feeding. High temperatures and potential drought conditions introduce unique challenges that can easily damage the turf. Proper summer fertilization requires careful consideration of timing and product selection to ensure the grass receives necessary nutrients without suffering from heat-induced stress or fertilizer burn. Understanding the specific needs of your grass type is the foundation for maintaining a healthy, green lawn.
Why Summer Fertilization Requires Caution
Fertilizing turf during peak summer heat can be risky because the grass plant is already under significant environmental stress. High temperatures can force grass, especially cool-season varieties, to enter a protective state of dormancy, where growth slows dramatically to conserve energy. Applying nitrogen fertilizer during this period attempts to force growth, which is counterproductive and harmful to the plant’s overall health.
The primary danger is fertilizer burn, which occurs when high concentrations of soluble salts in the fertilizer pull water out of the grass blades, essentially dehydrating them. Fertilizers containing quick-release nitrogen are particularly prone to causing this scorching effect, leading to unsightly brown patches. Furthermore, extreme heat hinders the grass’s ability to efficiently absorb and process nutrients, meaning that much of the applied fertilizer may be wasted or cause damage. Excessive top growth stimulated by fertilizer can also tax the root system further.
Recommended Frequency Based on Grass Type
The frequency of summer fertilization depends on whether your lawn is composed of cool-season or warm-season grass varieties. Cool-season grasses, such as Kentucky bluegrass, tall fescue, and perennial ryegrass, struggle in the summer heat. These grasses enter a semi-dormant state when temperatures consistently exceed 85°F, and therefore, they should receive little to no nitrogen fertilizer during the hottest months of July and August.
If you are consistently irrigating a cool-season lawn to prevent dormancy, you may consider a very light, preventative application to maintain health. This application should be low in nitrogen and focused on stress tolerance, rather than stimulating aggressive growth. The bulk of the cool-season lawn’s feeding should be reserved for the cooler, actively growing periods of early spring and, most importantly, late summer and fall.
Warm-season grasses, like Bermuda, Zoysia, and St. Augustine, thrive in high temperatures and are actively growing throughout the summer. These varieties require more frequent feeding during this period to sustain their vigorous growth and dense turf quality. For these lawns, a typical summer schedule involves applying fertilizer approximately every six to eight weeks, starting from late spring and continuing through early fall.
Some turf management professionals recommend a “spoon-feeding” approach for warm-season lawns, which involves applying very low rates of nitrogen more frequently, such as every two to four weeks. This steady, light feeding minimizes the risk of burn and nutrient runoff while continuously supporting the grass during its peak growth cycle. Fertilization should be avoided when daytime temperatures climb above 90°F to prevent heat stress.
Selecting the Right Nutrients for Summer Growth
When summer feeding is necessary, selecting a fertilizer with the correct nutrient composition prevents damage and promotes health. The nitrogen source should primarily be a slow-release formulation. Slow-release nitrogen provides steady, controlled feeding over several weeks, preventing the sudden growth surge and high salt concentration that cause turf burn.
The NPK ratio (Nitrogen, Phosphorus, and Potassium) should be tailored for summer stress. A summer fertilizer often features reduced nitrogen and a higher concentration of potassium. Potassium is valuable because it helps regulate internal plant functions, improving the grass’s tolerance to drought, heat, and disease.
A suitable summer NPK ratio might look like 10-0-20, with a low first number and a higher third number. While nitrogen promotes green color and leaf growth, potassium (K) supports root strength and cell wall integrity. Micronutrients, such as iron, can also be included to enhance green color without forcing excessive top growth, helping the turf cope with environmental stressors.