The practice of “Weed and Feed” (W&F) involves using a single product that combines fertilizer with an herbicide, offering a convenient way to nourish turf while controlling unwanted plants. This dual-action approach requires highly specific timing because the needs of the grass and the vulnerability of the weeds occur at different points in the season. For Wisconsin’s climate, which features distinct, short seasons and cool-season grasses, precision in application is the most important factor for success. Applying the product at the wrong time can fail to kill weeds or damage the desirable turf by promoting growth during stressful periods.
Understanding Timing Based on Soil Temperature
The success of a Weed and Feed application is dictated not by the calendar date or air temperature, but by the temperature of the soil itself. This measurement controls the biological processes of both the grass and the weeds. Weed and Feed products contain two types of herbicides: pre-emergent, which prevents weed seeds from sprouting, and post-emergent, which targets weeds already growing above ground. Each type requires different environmental conditions to work correctly.
The critical temperature to monitor is the point at which crabgrass, the most common spring weed, begins to germinate. This occurs when the soil temperature at a two-inch depth consistently remains between 50 and 55 degrees Fahrenheit for several consecutive days. Applying a pre-emergent W&F formulation just before this threshold establishes a chemical barrier that stops the crabgrass seed from emerging. Applying the product too early can cause its effectiveness to break down before germination, leaving the lawn unprotected later in the season.
The fertilizer component supports the cool-season grasses typical of Wisconsin, such as Kentucky bluegrass and fescue. These grasses thrive in cooler temperatures and enter a semi-dormant state during the heat of summer. The goal of fertilizing is to support growth during the spring and fall, when they are naturally active, and avoid pushing growth when they are stressed. Correctly timing the fertilizer ensures the grass utilizes nutrients to build strong roots and density, helping it naturally crowd out future weeds.
Wisconsin’s Seasonal Application Guide
The first application of Weed and Feed in Wisconsin should focus on pre-emergent crabgrass control in the spring. This window typically opens around mid-April in Southern Wisconsin and extends into early May further north. A reliable natural indicator is when forsythia shrubs are in full bloom, which usually aligns with the soil reaching the 50-degree mark. This application must contain a pre-emergent herbicide to create the necessary barrier before crabgrass germination begins.
The timing of this initial spring application must also balance the need for pre-emergent weed control with feeding the grass. A combination W&F product should be applied only after the cool-season grass has broken dormancy and has been mowed at least once. Applying fertilizer too early risks promoting a flush of top growth at the expense of root development.
The second application, focusing on post-emergent weed control and feeding, should occur six to eight weeks after the initial spring treatment. This places the application in late May or early June, when broadleaf weeds like dandelions and clover are actively growing and highly susceptible to post-emergent herbicides. The fertilizer supports the grass as it enters the stressful summer period, encouraging density to help it compete against remaining weeds.
The most important feeding for Wisconsin cool-season turf occurs in the fall, with the final application window in early September, around Labor Day. This fall application, often called winterization, encourages deep root growth and the storage of carbohydrates for winter survival and a strong spring green-up. While a W&F product can be used if broadleaf weeds like dandelions are present—fall is the most effective time to kill them—the focus is primarily on the high-nitrogen fertilizer. A second, later fall feeding (late October) is often recommended, but should be fertilizer-only to avoid stimulating grass growth too close to the first deep freeze.
Ensuring Effective Application
Once the correct timing has been determined, the execution of the application is the next step. To ensure the best results, the lawn should be mowed one or two days before spreading the granular product. This prepares the grass blades for optimal herbicide contact and allows the granules to reach the soil surface more effectively.
Most granular Weed and Feed products containing post-emergent herbicides require the weed foliage to be moist or damp upon application. The herbicide granules must stick to the leaves of actively growing weeds, such as dandelions, for the chemical to be absorbed and translocated to the roots. Applying the product while the morning dew is still present is an effective technique for achieving this necessary moisture.
After the product has been spread, it is crucial to allow a waiting period before the lawn is watered or before rainfall occurs. This period is typically 24 to 48 hours and allows sufficient time for the post-emergent herbicide to be absorbed by the targeted weed leaves. Watering too soon will wash the product off the leaves, significantly reducing its effectiveness. Finally, always calibrate the spreader to the setting recommended on the product label to ensure an even application rate and prevent the risk of over-fertilizing, which can chemically burn the turf.