Weed and feed products combine fertilizer to nourish grass with a selective herbicide to control broadleaf weeds. While this combination saves time, precise irrigation timing determines the treatment’s success. Watering too soon can wash the herbicide away, making weed control ineffective, while waiting too long prevents the fertilizer from properly activating in the soil. The specific waiting period depends on the product formulation, as granular and liquid types require distinctly different post-application care. Always follow manufacturer directions to ensure the product works as intended and prevents turf damage.
Immediate Watering for Granular Products
Granular weed and feed products contain a post-emergent herbicide designed to target existing weeds by sticking directly to their leaves. To facilitate this adhesion, the lawn must be damp before application, often achieved by applying the product when dew is present or after a light pre-watering. Once the granules are spread, the most important instruction is to avoid immediate irrigation.
Watering too soon will wash the herbicide granules off the weed foliage and down into the soil before the chemicals have had time to absorb into the plant cells. This runoff significantly reduces the effectiveness of the weed-killing component. The granular herbicide needs contact time with the weed’s surface to begin the process of absorption, which is how it ultimately travels to the root system to eliminate the plant.
The necessary waiting period for granular products typically ranges from 24 to 72 hours following application. This delay allows the active ingredients in the granules to transfer from the pellet to the leaf cuticle of the targeted weeds. If the product contains post-emergent weed killer, a waiting period of 48 hours is frequently recommended to ensure maximum absorption and control.
If heavy rain occurs shortly after application, it can displace the undissolved granules, which may lead to patches of over-fertilization and untreated weeds. Conversely, waiting too long to introduce water, especially in dry conditions, allows the fertilizer salts to concentrate on the surface. This concentration increases the risk of burning the grass, so the waiting period is a careful balance between allowing the herbicide to work and protecting the turf.
Watering After Liquid Spray Applications
Liquid weed and feed applications, typically applied via a sprayer, require a different approach to post-application watering. Unlike granular products that need moisture to stick, liquid herbicides are designed to be absorbed directly through the leaves of the weeds. The primary concern after a liquid application is ensuring the product has fully dried and penetrated the weed’s foliage before any moisture is introduced.
The recommended waiting period for liquid treatments is generally 24 to 48 hours, or until the product is completely dry on the leaf surface. Premature watering or rainfall will dilute the herbicide, causing it to run off the leaves and rendering the application largely ineffective. The liquid formulation needs time to permeate the plant’s vascular system for a successful kill.
Monitoring the local weather forecast is important for liquid products. A dry window of at least 24 hours is needed after spraying to guarantee proper foliar absorption. If the liquid product is washed off prematurely, the weed control benefit is lost, and the application must be repeated to achieve the desired results.
Resuming the Regular Watering Schedule
Once the necessary waiting period for the herbicide to work has passed, introduce water to activate the fertilizer component of the product. The fertilizer granules must dissolve, or the dried liquid must be washed into the soil, so the nutrients can be absorbed by the grass roots. This initial watering should be thorough, aiming for approximately one-half to one inch of water across the treated area.
A deep, soaking irrigation helps to move the nitrogen, phosphorus, and potassium into the root zone. This action activates the fertilizer and helps dissolve any remaining surface salts from the application, which minimizes the potential for fertilizer burn. Using a rain gauge or a straight-sided container can help measure the amount of water applied to ensure sufficient depth without causing wasteful runoff.
Following this activation watering, the lawn should transition back to its standard irrigation schedule to maintain turf health and maximize the fertilizer’s benefit. Consistent moisture allows the fertilizer to continue feeding the grass over time, promoting the strong root growth necessary for a dense, healthy lawn.