Watering in fertilizer is a precise action that ensures applied nutrients are available to plants and prevents chemical damage. This process involves using water immediately after application to move nutrients from the surface of the soil or lawn down into the root zone. The primary objectives are to activate the fertilizer particles so they begin dissolving and to dilute the concentrated salts. Proper watering transitions the fertilizer from a granular product to a nourishing solution accessible to roots.
Why Watering In is Essential for Granular Products
Granular fertilizers are concentrated mineral salts necessary for plant growth. These solid particles must dissolve in water before roots can absorb them, making water application the initial step in nutrient activation. The water acts as the solvent, breaking down the granules and creating a nutrient solution that travels through the soil profile toward the roots.
The most pressing reason for immediate watering is to prevent fertilizer burn. This damage occurs because the high concentration of soluble salts in the granules creates an osmotic imbalance near the plant roots. If the salt concentration outside the roots is significantly higher than inside, osmosis causes water to flow out of the plant cells and into the soil. This reversal leads to rapid cellular dehydration, appearing as scorching or browning on the leaves and grass blades.
Applying water immediately after spreading granular fertilizer effectively dilutes the high salt concentration at the surface. By dissolving the granules and moving them deeper into the soil, the water minimizes direct contact between the concentrated salts and the plant’s crown and foliage. Deep watering ensures nutrients are distributed across a larger volume of soil, preventing the dehydration that characterizes fertilizer burn.
Step-by-Step Guide for Activating Fertilizer
The correct timing for watering in granular fertilizer is immediately after spreading, ideally within a few hours. Waiting too long, especially during hot, dry weather, allows the concentrated salts to sit on the turf or soil and increase the risk of leaf scorch. If the application is timed before a light rain, the rainfall can handle the watering-in step, but heavy downpours should be avoided as they can cause runoff and nutrient loss.
The depth of water applied is more important than the duration, and a light sprinkling is inadequate for activation and burn prevention. The goal is a deep, soaking irrigation to move the nutrients past the surface layer and into the root zone. For a lawn, this generally means applying between a quarter-inch and a half-inch of water, which is often enough to moisten the soil a few inches deep. This depth can be measured by placing empty tuna cans or similar containers in the application area and stopping irrigation when they have collected the target amount of water.
The time required depends on the soil type and the watering tool used, such as a sprinkler or hose-end sprayer. Clay soils absorb water slowly, requiring a longer duration of watering to prevent runoff, but they hold moisture longer, meaning less frequent watering is needed. Sandy soils allow water to drain quickly, so they may require a shorter total duration but potentially need more frequent irrigation cycles. The final indicator of successful watering is soil moisture that penetrates 3 to 4 inches below the surface, which can be checked with a screwdriver.
Managing Water After Applying Liquid or Soluble Feeds
Liquid and water-soluble fertilizers are applied already dissolved in water, changing the post-application watering approach. Since the nutrients are already in a mobile solution, the primary concern shifts from activation and dilution to retention and absorption. For fertilizers applied as a soil drench, heavy follow-up watering should be avoided.
Immediate, heavy irrigation after a soil drench can cause the applied nutrients to leach below the root zone, wasting the product. The liquid fertilizer is already positioned for root uptake, so a return to the regular watering schedule is appropriate, avoiding any additional deep soak.
When applying a foliar feed, the product is sprayed directly onto the leaves for absorption. These products require a drying time to allow nutrients to be taken up by the leaf surface before being washed away. Watering should be delayed for several hours, typically 2 to 24 hours, to ensure the plant has sufficient time to absorb the feed. After the necessary absorption period, a light rinse can wash remaining residue from the leaves into the soil for root absorption.