Applying granular “Weed and Feed” delivers nutrients and controls weeds simultaneously, but relies on following manufacturer instructions, especially regarding water. The product combines dry, granular fertilizer and herbicide. Without the crucial watering step, neither component works effectively, risking damage to the grass while failing to eliminate weeds.
The Dual Role of Water in Product Activation
Water acts as the catalyst for both the fertilizer and herbicide components. For the fertilizer, water dissolves the solid pellets, allowing nutrient compounds to move into the soil. Once dissolved, the nitrogen, phosphorus, and potassium are carried down into the root zone, where they are absorbed for growth and color.
The herbicide component also requires moisture for activation. Granular herbicides designed to kill existing weeds need water to help the active ingredients adhere to the broadleaf weed foliage. Pre-emergent herbicides, which prevent weed seeds from sprouting, must be watered into the soil to create the necessary chemical barrier that halts germination. Without this moisture, the active ingredients remain dry and ineffective on the soil surface or grass blades.
The Immediate Threat of Fertilizer Burn
The most immediate consequence of failing to water in granular “Weed and Feed” is chemical burn, often called “salt burn.” Fertilizer granules are composed of nutrient salts. When these dry salts sit directly on grass blades, they create a highly concentrated environment. This initiates osmosis, where water moves from the grass cells (low concentration) toward the salts (high concentration).
The fertilizer granules draw moisture out of the grass cells, dehydrating and damaging the leaf tissue. The resulting damage appears as yellowing, browning, or scorched patches, particularly where granules were heavily concentrated. This process is exacerbated by environmental factors such as high heat or intense sunlight, which increase the grass’s moisture demands. Leaving the granules unwatered allows this destructive dehydration to continue until moisture is introduced.
Why the Herbicide Component Fails
The weed-killing action is severely compromised without proper watering. Most granular weed and feed products contain post-emergent herbicides designed to control visible weeds like dandelions and clover. These herbicides require the granules to stick to the moist surface of the broadleaf weed so the chemical can be absorbed through the foliage.
If the lawn is dry when applied and remains dry, the smooth granules roll off the weed leaves onto the soil. This lack of adhesion prevents the herbicide from being taken up, causing the control mechanism to fail. For pre-emergent herbicides, water is needed to dissolve the granules and carry the active ingredient into the top layer of soil. Without this, the necessary chemical barrier is never established, allowing weed seeds to germinate and grow.
Immediate Corrective Steps
If you realize you applied “Weed and Feed” but have not watered it in, immediate action is necessary to mitigate damage. The primary goal is to dissolve the fertilizer salts and wash them off the grass blades and into the soil. Begin a deep watering session as soon as possible, ideally within 12 to 24 hours, to minimize osmotic stress on the turf.
Apply about a half-inch of water across the entire lawn using a sprinkler system to ensure even coverage. This deep irrigation helps break down the granules and move concentrated salts away from the sensitive crown and leaf tissues of the grass. Monitor the lawn over the next few days for signs of burn, and maintain a regular watering schedule to help the grass recover. If visible damage is widespread, continued deep watering can leach the remaining excess salts further down past the root zone.