The answer to whether you water after applying a granular “weed and feed” product is yes, but not right away. This popular lawn care product combines granular fertilizer with a broadleaf herbicide in a single application. The dual nature of the product causes confusion because the two components have conflicting moisture requirements for proper activation. Successful application requires a precise, two-part watering strategy to support both the weed-killing and fertilizing actions.
The Dual Mechanism of Weed and Feed
The product’s success relies on separate mechanisms for its two active ingredients: the fertilizer and the herbicide. The fertilizer component, a blend of nutrients, must dissolve into the soil to become available for absorption by the turfgrass root systems. The granular herbicide is typically a post-emergent selective weed killer that targets weeds that have already sprouted. For the chemical to be effective, the granules must physically stick to the foliage of broadleaf weeds, allowing the herbicide to be absorbed through the leaves.
Pre-Application Watering
The first step in the watering process happens before the product is spread across the lawn. The primary purpose of this pre-application moisture is to ensure the granular herbicide adheres to the weed foliage, which is the mechanism for killing the weeds. If the grass and weeds are completely dry, the granules will fall onto the soil surface and cannot be properly absorbed. The lawn should be lightly dampened, aiming for a dewy surface rather than a saturated one. Many professionals suggest applying the product early in the morning when natural dew is present, as this provides the perfect level of moisture for the herbicide to remain in direct contact with the weed’s leaves.
Post-Application Watering Timing and Purpose
After spreading the weed and feed, the second phase of watering involves a calculated delay. Watering immediately will wash the herbicide off the weed leaves and into the soil, rendering the weed-killing component ineffective. Manufacturers recommend waiting 24 to 48 hours to allow the broadleaf weeds sufficient time to absorb the chemical. Once this waiting period has passed, watering is necessary to activate the fertilizer component. Applying water dissolves the nutrient salts and carries them down into the root zone, ensuring the grass roots can access the nutrients for growth. About one-quarter to one-half inch of water is generally needed to fully dissolve the fertilizer.
Consequences of Improper Watering
Ignoring the two-step watering protocol can lead to several undesirable outcomes for the lawn. Watering too soon prematurely washes the herbicide off the leaves, diluting the chemical and allowing weeds to survive. Applying water too late, or not at all, can lead to a condition known as “fertilizer burn.” Fertilizer burn occurs because the granules are composed of nutrient salts, which have a dehydrating effect on plant tissue. If the granules remain highly concentrated without being dissolved by water, the high salt concentration draws moisture out of the grass cells through osmosis, causing the blades to turn brown and crispy.