Homeowners often use “weed and feed” products for lawn maintenance. This popular product offers a greener yard while simultaneously eliminating common broadleaf invaders. The most frequent question concerns the timeline for seeing dead weeds. The process is neither instantaneous nor uniform, depending on chemistry and environmental factors.
The Dual Function of Weed and Feed
The product gets its name from its two components: a fertilizer (“feed”) and a selective herbicide (“weed” killer). The fertilizer is rich in nitrogen, promoting lush growth in turfgrass. This nitrogen boost is also absorbed by the weeds, which accelerates the absorption of the herbicide.
The herbicide component, often containing compounds like 2,4-D, Dicamba, or MCPP, targets broadleaf weeds (dicots). These chemicals are synthetic auxins, acting as plant growth hormones absorbed through the foliage. The fertilizer encourages vigorous growth, accelerating the systemic transport of the herbicide throughout the plant’s vascular system.
Fueled by nitrogen, this increased metabolic activity causes the selective herbicide to be translocated quickly to the weed’s roots and growing points. The systemic action results in uncontrolled and distorted cell growth, causing the weed to grow itself to death. This formulation is ineffective against grassy weeds, such as crabgrass, which are monocots.
Timeline for Visible Weed Death
The first visible signs that the systemic herbicide is working usually appear within seven to fourteen days following application. During this initial period, weeds show physical distortions, such as the curling or twisting of leaves and stems (epinasty), indicating disruption of normal plant function.
Following these distortions, discoloration begins as the plant’s ability to transport nutrients and water is compromised. Weeds start to yellow (chlorosis) or turn brown (necrosis) as tissues die off. Complete collapse, indicating full root-to-tip death, generally requires three to four weeks.
The total time depends significantly on the size and health of the plants. Small, young weeds may collapse closer to the two-week mark. Established, deep-rooted perennials may take the full four weeks to succumb, as the systemic action needs time to reach the entire root structure.
Key Factors Influencing Herbicide Speed
The speed at which a weed and feed product delivers results is influenced by the environment and the weeds themselves.
Temperature and Moisture
Temperature is a primary environmental factor, as the herbicide’s effectiveness is maximized when weeds are actively growing. The ideal range for application is when temperatures are consistently between 65°F and 85°F. If temperatures are too low, the weeds are semi-dormant, and their metabolic activity slows down, preventing efficient absorption. Conversely, if temperatures exceed 90°F, the grass can become stressed, and the herbicide may volatilize, reducing effectiveness or damaging non-target plants. The granular product also requires moisture, such as dew or a light film of water, on the leaves to ensure the particles stick to the foliage.
Weed Maturity
The maturity and type of weed significantly affect kill time. Younger, small broadleaf weeds are highly susceptible because they are actively growing and have less mass for the chemical to saturate. Older, established weeds, such as mature dandelions or plantain with substantial root systems, present a greater challenge and require more time for the herbicide to travel throughout the entire plant and achieve a complete kill.
Optimizing Application for Fastest Results
To achieve the quickest and most effective results, focus on optimizing the timing and preparation of the application. The product must be applied when weeds are in a state of active growth, meaning they are vigorously photosynthesizing and pulling nutrients through their leaves, to ensure maximum uptake of the herbicide.
Applying the granular product when the weed foliage is wet, such as in the early morning dew, is necessary for the particles to adhere properly to the leaves. Adherence is critical for absorption, as the chemical must be taken in through the leaf surface.
It is beneficial to avoid mowing the lawn for one to two days both before and after application. Skipping the mow allows the weeds to maintain maximum leaf surface area, providing a larger target for the granules to stick to and be absorbed.
After application, avoid heavy irrigation or natural rainfall for twenty-four to forty-eight hours. This period allows the herbicide to remain concentrated on the leaves long enough to be fully absorbed before being washed into the soil, where its weed-killing potency is diminished.