Weed and Feed (W&F) products combine lawn fertilizer and broadleaf herbicide to simplify turf maintenance. The fertilizer supplies nutrients to the grass, while the herbicide targets unwanted plants like dandelions and clover. Determining when to mow after application is the most common question homeowners have, and the answer is driven entirely by the product’s formulation. Waiting the correct amount of time ensures the weed-killing chemicals are fully effective. The required waiting period varies significantly depending on whether the product is applied as a dry, granular pellet or a liquid spray.
Mowing Timing for Granular Applications
Granular Weed and Feed products require a specific application process to ensure the herbicide component works correctly. These products rely on the herbicide adhering to the surface of the weed’s foliage, not the soil, before it can be absorbed. For this to happen, the lawn surface must be wet either from morning dew, a light watering beforehand, or a light rain immediately after application.
The recommended waiting period before mowing after a granular application is typically 24 to 48 hours. Mowing too quickly physically removes the granule and the attached herbicide from the weed leaf. This action cuts off the delivery system before the chemical has a chance to enter the plant. If the granules are still visible on the leaf surface, the lawn should not be mowed yet.
The fertilizer portion also benefits from this waiting period, as it needs time to dissolve and move into the soil. Mowing immediately after applying a granular product, especially with a bagging mower, risks vacuuming up the undissolved pellets. Waiting the full 48 hours allows the herbicide to transfer to the weed surface and permits the fertilizer to begin soaking into the turf.
Mowing Timing for Liquid Spray Applications
Liquid Weed and Feed applications are typically mixed with water and sprayed directly onto the weeds. The initial concern is the “dry time,” which is the period when the herbicide is wet and can be easily washed off or rubbed away. This dry time is often only two to four hours, after which the surface is safe for foot traffic or pets.
The time required for the herbicide to be fully absorbed by the weed is much longer than the simple dry time. For most liquid products, the minimum waiting period before mowing is 24 hours, though a 48-hour window provides maximum effectiveness. Mowing during this critical absorption window can still remove the treated leaf tips, which contain the concentrated herbicide, before it has fully moved throughout the plant structure.
The Mechanism: Why Waiting is Necessary
A delay is necessary because most modern broadleaf herbicides are systemic, meaning they must travel through the plant to reach the site of action. The application process relies on the leaves, or foliage, to act as the absorption point for the chemical.
Once absorbed through the leaf’s waxy cuticle, the herbicide is transported through the weed’s vascular system, specifically the phloem. This transport process, known as translocation, is slow and can take a full day or more to move the chemical down to the roots and growth points. The chemical must reach the root system to achieve a complete kill.
Mowing too soon removes the portion of the plant that absorbed the chemical before translocation is complete. This results in “tip burn,” where exposed leaves die back, but the root remains alive and capable of regrowing the weed. Allowing the full 24 to 48 hours ensures the systemic herbicide moves to the roots, successfully killing the entire weed and preventing future regrowth.