Determining whether to apply fertilizer to wet or dry grass is a common dilemma. The moisture level of the turfgrass blades significantly influences how effectively the nutrients reach the soil and whether the lawn sustains chemical damage. The correct approach is not universal, as the answer hinges primarily on the physical form of the product being used—specifically, whether the fertilizer is granular or liquid.
The Core Rule: Matching Application to Fertilizer Type
The most important factor is the physical composition of the fertilizer being applied. Granular fertilizers, which are solid pellets containing concentrated salts, require the turfgrass blades to be completely dry. Applying these granules to wet foliage causes them to stick to the leaf surface instead of filtering down to the soil level.
When granules remain stuck on wet blades, they dissolve prematurely and concentrate their high salt content in small areas. This localized concentration leads to uneven feeding and creates an elevated risk of phytotoxicity, commonly known as fertilizer burn. Dry blades ensure the pellets bounce off the foliage and settle directly onto the soil surface for root absorption.
Liquid fertilizers, applied via a spray, offer slightly more flexibility regarding blade moisture. These products are often formulated for both root absorption and foliar feeding, allowing the grass to absorb nutrients directly through the leaves. For optimal foliar uptake, the blades should be dry or only slightly damp with dew, allowing the liquid to adhere to the leaf surface without running off.
If the blades are saturated with water, the liquid fertilizer will become overly diluted and wash away quickly, reducing the concentration of nutrients delivered. However, the soil beneath the turf should possess a mild amount of moisture to facilitate immediate root uptake once the liquid reaches the ground. This distinction between blade moisture and soil moisture is a nuanced part of successful liquid application.
Pre-Application Preparation and Timing
Successful fertilization begins with proper lawn preparation a day or two before the application. Mowing the lawn 24 to 48 hours prior is necessary, as shorter grass ensures the fertilizer material can easily filter through the canopy and settle close to the soil line. This step reduces the chance of the granules or liquid being trapped by longer blades.
The timing of the application should also be carefully considered to minimize environmental stress on the grass. Applying fertilizer during the cooler periods of the day, such as the early morning or late evening, is recommended to prevent the rapid evaporation of moisture. High temperatures can exacerbate the drying effect of high-salt fertilizers, increasing the potential for chemical scorching on the turf.
Checking the weather forecast is important, primarily to avoid unexpected heavy rainfall immediately after application. Intense downpours can wash away granular products before they dissolve and activate, leading to wasted product and nutrient runoff. Conversely, the soil should not be completely desiccated before the application, as a slightly moist base enhances the initial absorption of nutrients once the fertilizer is watered in.
Immediate Post-Application Steps
Once the fertilizer has been distributed across the dry turf blades, immediate action is required to activate the product and protect the grass. For almost all granular fertilizers, prompt and thorough watering is mandatory to initiate nutrient release. This irrigation dissolves the outer coating of the granules, allowing the encapsulated nutrients to seep into the soil solution for root uptake.
The secondary function of immediate post-application watering is to prevent fertilizer burn. High concentrations of nitrogen salts can exert an osmotic pressure, drawing moisture out of the grass cells in a process called desiccation. By washing the fertilizer residue off the blades and into the soil, this potential for chemical scorching is minimized.
The amount of water applied must be sufficient to dilute the salts and move the nutrients into the root zone without causing saturation. A general guideline is to apply about one-quarter to one-half inch of water across the treated area. This amount is enough to fully dissolve the granules and carry the product below the soil surface. Watering should be done gently to avoid creating surface runoff, which carries valuable nutrients away from the lawn and into storm drains.
Overwatering is counterproductive because it can leach the dissolved nutrients too deeply below the root zone, making them inaccessible to the grass. The goal is a measured, uniform application that activates the product without causing nutrient loss or excessive soil saturation. Final steps include cleaning the application equipment, such as spreaders, to prevent corrosion.