The convenience of a single product that both nourishes the lawn and eliminates weeds has made “Weed and Feed” popular. This combination contains a broadleaf herbicide and a fertilizer blend, often rich in nitrogen, to promote grass growth. The success of this dual-action treatment depends entirely on precise application timing. This article focuses on the specific conditions and seasonal windows necessary to maximize the product’s effectiveness.
Understanding the Components of Weed and Feed
The primary function of the “feed” component is to deliver essential nutrients, typically nitrogen, phosphorus, and potassium, to the turf. Nitrogen encourages rapid green-up and dense growth, helping the grass outcompete weeds for resources. The fertilizer often includes both fast-release nutrients for immediate effect and slow-release components for sustained feeding.
The “weed” component is a selective herbicide designed to kill broadleaf weeds without harming the grass. Products use either a pre-emergent or a post-emergent herbicide, or sometimes both. Pre-emergent herbicides prevent weed seeds from germinating. Post-emergent herbicides, which are common in granular Weed and Feed, target weeds that are already actively growing, such as dandelions and clover. Pre-emergent products must be applied before germination, while post-emergent products must be applied directly to existing weeds.
Optimal Seasonal Timing for Application
The ideal time for application is early spring and early fall, when temperatures are moderate and the turf is actively growing. Applying during these windows ensures the grass absorbs the fertilizer while weeds are most vulnerable to the herbicide.
Early spring application is necessary for pre-emergent control of summer annual weeds like crabgrass. The product must be applied when the soil temperature is consistently between 50°F and 55°F, measured at 2 to 4 inches deep. This range signals the beginning of crabgrass seed germination, establishing the final window for a protective barrier.
If the product contains a post-emergent herbicide, spring timing shifts to when weeds are visible and actively growing, generally above 60°F air temperature. Fall application, from late August through early October, targets cool-season weeds. This timing strengthens the grass’s root system, helping the turf withstand winter dormancy and promoting earlier green-up the following spring.
Required Lawn Conditions for Effective Use
For post-emergent granular Weed and Feed to be effective, the grass must be damp at the time of application. The herbicide granules need to stick to the broadleaf weed foliage so the active ingredients can be absorbed through the leaf surface. Applying the product when the grass is wet with dew or lightly moistened ensures maximum contact and absorption.
The timing relative to mowing is also a factor. It is advisable to mow the lawn two to four days before applying the product. This allows the weeds to grow back slightly, providing more leaf surface area for the herbicide granules to adhere to.
After application, refrain from mowing for at least 24 to 48 hours to give the herbicide time to enter the weed’s vascular system. Similarly, delay watering or rainfall for a minimum of 24 hours, and preferably up to 48 hours. Premature irrigation washes the granules off the leaves before the herbicide is absorbed, significantly reducing effectiveness.
Common Timing Mistakes to Avoid
A frequent mistake is applying the product during the extreme heat of mid-summer. Most Weed and Feed products should not be applied when air temperatures are consistently above 85°F to 90°F. The combination of high heat and the nitrogen-rich fertilizer can severely stress the grass, causing chemical burn or scorching the turf.
Another timing error involves applying the product too close to a reseeding or overseeding project. The pre-emergent herbicides are non-selective to seeds and will prevent new grass seed from germinating. A waiting period of at least four to six weeks is required between the application of Weed and Feed and the planting of new grass seed.
Applying the product just before a heavy rain is also counterproductive. While light moisture is required for the granules to stick, a downpour within 24 hours washes the herbicide off the leaves. This premature dilution and displacement renders the weed control ineffective and may contribute to nutrient runoff.