Weed and Feed products combine fertilizer, which nourishes your lawn, with a selective herbicide designed to eliminate broadleaf weeds without harming the grass. Understanding the timeline for weed control is often challenging because the process is not instant, depending heavily on the underlying science of how the herbicide functions. This realistic timeframe for elimination helps set proper expectations for lawn care efforts.
The Mechanism of Weed Control
The weed-killing component in these products typically uses systemic herbicides that are applied directly to the weed foliage. Systemic herbicides must be absorbed by the leaves to work effectively. Once absorbed, the chemical begins its journey through the plant’s vascular system.
The herbicide must travel through the plant, a process called translocation, to reach the root system. Many common herbicides used in these products are synthetic auxins, which mimic natural plant growth hormones but at excessive levels.
This movement is necessary because simply killing the leaves of a perennial weed will not eliminate the plant; the root system stores energy and can generate new growth. For a complete and lasting kill, the chemical must successfully travel down to the roots to interrupt the plant’s functions entirely. The death of the weed is an inherently slow, internal process rather than an immediate external one.
Expected Timeline for Visible Results
Homeowners can generally expect to see the first signs of stress in treated weeds within 3 to 7 days after a successful application. These initial symptoms often manifest as the curling, twisting, or wilting of the weed’s leaves and stems as the growth-regulating herbicide begins to take effect.
Visible discoloration, such as yellowing or browning of the foliage, typically becomes apparent between 7 and 14 days following the initial application. While the weed may look severely damaged at this point, the root system may still be alive, especially for mature or deep-rooted varieties. The full efficacy, which involves the complete death of the root structure, usually requires 14 to 21 days or sometimes longer for tougher perennial weeds.
Even if the weeds appear entirely brown or dead after two weeks, allowing the product to work for the full three-week period ensures the chemical has fully translocated and achieved a complete root kill. Patience is necessary, as attempting a second application too soon can be ineffective and may risk damaging the surrounding turf.
Key Factors Influencing Herbicide Speed
Active Growth and Temperature
Several external conditions significantly influence how quickly a systemic herbicide can kill a weed, primarily by affecting the rate of absorption and translocation. The product works most efficiently when the weeds are actively growing.
Temperature plays a major role, as herbicides perform best in moderate warmth, typically when temperatures are between 65°F and 85°F. Applying the product during periods of very high heat, such as above 90°F, can stress the weed and cause it to shut down its growth processes, slowing or stopping the herbicide’s movement and reducing effectiveness.
Moisture Requirements
Proper moisture is also essential for the granular form of Weed and Feed products, which require the herbicide granules to adhere to the moist surface of the weed’s leaves. Applying the product to a lawn with morning dew or lightly moistened foliage ensures the chemical can stick and be absorbed. Conversely, watering the lawn or having heavy rainfall immediately after application can wash the herbicide off the leaves before absorption is complete, rendering the treatment ineffective.
Weed Type and Maturity
The type and maturity of the weed also determine the speed of elimination. Broadleaf weeds like dandelions often show results faster than tougher, more persistent weeds such as clover or creeping vines, which have denser structures or more extensive root systems. Younger, less established weeds absorb and translocate the chemical much faster than large, mature weeds.