A “weed and feed” product is a combination of two distinct lawn care treatments: a granular fertilizer designed to nourish the turfgrass and a broadleaf herbicide intended to eliminate weeds. The question of whether to apply this product during the summer is complex, as the effectiveness and safety are highly dependent on the current air temperature, soil moisture, and the specific type of grass in your lawn. While the convenience of a single application is appealing, applying this combination product in the summer often carries significant risks that outweigh the potential benefits due to the biological response of turfgrass to heat.
Why Summer Application is Risky
Summer heat naturally imposes a significant metabolic burden on turfgrass, causing it to slow its growth rate and conserve energy, sometimes entering a state of semi-dormancy. When grass is already under this heat-induced stress, the addition of a high-nitrogen fertilizer can be severely detrimental. Fast-release nitrogen, in particular, forces the stressed plant to push new growth when its energy reserves are already depleted, which can further weaken the root system.
The high concentration of salts in the fertilizer draws moisture directly out of the grass blades, leading to a scorched, yellow, or brown appearance known as fertilizer burn. Because a stressed lawn is less able to absorb and process nutrients, the excess nitrogen remains on the surface, dehydrating the tissue it touches.
The herbicide component also faces challenges in hot weather, primarily concerning reduced efficacy and potential volatility. Weeds respond to high heat by developing a thicker, waxy outer layer (the cuticle) to minimize water loss. This layer prevents the weed killer from being properly absorbed. Furthermore, temperatures consistently above 85°F can cause some active herbicide ingredients to volatilize, turning into a gas that drifts off the target area and potentially damaging desirable plants.
Essential Application Adjustments
The single most important factor is the ambient temperature. Most product labels advise against applying when temperatures are consistently forecast to exceed 85°F for 24 to 48 hours following application. Applying the product only during the cooler parts of the day, such as the early morning or late evening hours, can temporarily reduce the immediate risk of burn and volatility.
A precise watering protocol is non-negotiable for summer applications. Apply the product to a dry lawn to prevent granules from sticking to and dissolving on the grass blades, which causes localized burn spots. Immediately after application, the lawn must be thoroughly watered to wash the fertilizer off the foliage and move the nutrients into the soil. This deep watering activates the fertilizer while protecting the grass surface.
Careful product selection further reduces the danger, particularly by choosing a formula that contains a high percentage of slow-release nitrogen. These coated fertilizers release their nutrients gradually over a period of six to eight weeks, which prevents the sudden, excessive surge of growth that stresses the plant. A slow-release formula ensures a more regulated delivery of nutrients, which is far safer for turf that is already managing the demands of summer heat.
Alternative Summer Lawn Care Strategies
The safest approach during the summer is to separate the “weed” and “feed” components, managing each task with a targeted, low-impact strategy. Instead of broadcasting a granular combination product across the entire lawn, weed control should be limited to spot-treating individual weeds or small patches. Selective liquid herbicides, applied directly to the unwanted plants, minimize the amount of chemical stress placed on the surrounding healthy turfgrass.
For the feeding component, a heavy fertilizer application should be postponed until the temperatures drop in the fall. If the grass is actively growing and not dormant, a light application of a low-nitrogen fertilizer that is higher in potassium can be used to support the plant’s internal stress tolerance. Potassium is beneficial for regulating water balance within the plant, which is advantageous during periods of high heat and potential drought.
Simple cultural practices provide a low-risk alternative to chemical feeding. Allowing the grass to grow taller by setting the mower deck to one of its highest settings encourages deeper root growth, improving the plant’s resilience to heat and drought. Leaving finely mulched grass clippings on the lawn also returns organic nitrogen and moisture to the soil naturally, providing a gentle and continuous feed until autumn.