Fertilizing a lawn during the summer months is confusing for homeowners because the answer is highly conditional. Applying nutrients when the weather is hot and dry can be either beneficial or severely damaging, depending on the specific type of grass and the product used. Successfully feeding your turf in mid-season requires careful consideration of temperatures and the grass’s natural growth cycle. Understanding when the grass is actively growing versus when it is dormant is the most important factor in preventing lawn injury.
The Core Rule: Fertilizing During Summer Dormancy
The primary risk of summer fertilization is heat stress and root burn caused by applying the wrong product at the wrong time. During extreme heat or drought, grass enters a state of dormancy, a survival mechanism where it conserves energy and growth slows or stops completely. Forcing the grass to grow using high-nitrogen fertilizer during this period is detrimental because the plant is focused on surviving the challenging conditions, not on producing new shoots.
Applying quick-release nitrogen to a struggling lawn can lead to chemical burn, often appearing as scorched, brown streaks or patches. This is particularly true when daytime temperatures consistently exceed 85 degrees Fahrenheit, which is the point where the metabolic processes of many grasses begin to slow down. The fertilizer salt content can draw moisture out of the grass blades, causing cellular damage and weakening the turf’s overall resilience if not immediately watered in. Therefore, always ensure the lawn is adequately hydrated before and after application. If your lawn is visibly brown and brittle from a lack of moisture, it is already dormant, and fertilization will be a wasteful and counterproductive effort.
Tailoring Your Approach by Grass Type
The decision to fertilize must be based on whether your lawn is a cool-season or warm-season variety, as their summer needs are fundamentally different.
Cool-Season Grasses
Cool-season grasses, which include Kentucky Bluegrass and various Fescues, thrive in temperatures between 50 and 65 degrees Fahrenheit. These grasses naturally struggle and may go dormant when high summer temperatures arrive, meaning their primary feeding seasons are spring and fall. Feeding cool-season turf heavily in mid-summer is discouraged, as it pushes growth when the plant is already stressed and trying to conserve resources. If a light application is necessary, it should be done with extreme caution and only when the turf is not showing signs of heat stress.
Warm-Season Grasses
In contrast, warm-season grasses such as Bermuda and Zoysia are actively growing in the summer heat, with ideal soil temperatures ranging from 70 to 90 degrees Fahrenheit. Summer is the peak growing period for these varieties, making it their main feeding season for maintaining density and color. These grasses can tolerate a consistent feeding schedule during the summer months to support their robust growth rate. For these types, a mid-summer application can be beneficial, but it must be applied correctly to avoid overwhelming the system.
Choosing the Right Summer Fertilizer
Regardless of the grass type, the composition of the product is paramount when feeding during the warmer months.
Slow-Release Nitrogen
It is important to select fertilizers that contain slow-release nitrogen, also known as controlled-release nitrogen. This formulation delivers nutrients gradually over several weeks or months, preventing the sudden surge of growth and the high burn risk associated with quick-release products. The slow, steady feeding supports sustained health without overstimulating the grass’s metabolic rate in the heat.
The Role of Potassium (K)
Another important component for summer turf health is Potassium (K), often listed as the third number in the N-P-K ratio on fertilizer bags. Potassium is crucial for enhancing the grass’s ability to manage environmental challenges like heat and drought. It works by strengthening the plant’s cell walls, which helps regulate water movement and reduces moisture loss through the leaves, a process known as transpiration. Including a higher percentage of potassium helps fortify the turf against the stresses of the summer environment.