When using a combined fertilizer and weed control solution, known as “weed and feed,” precise timing is crucial. This product has a dual function: the “feed” component delivers nutrients to the turfgrass, and the “weed” component uses herbicides to eliminate unwanted plants. Successful application requires precise seasonal timing to maximize the benefits of both ingredients. Ignoring the optimal windows can lead to wasted product, scorched grass, or ineffective weed control.
Understanding the Function of Weed and Feed
The precise timing relates to the mechanics of the herbicides used. Weed and feed products typically contain one of two main types of herbicide action: pre-emergent or post-emergent.
Pre-emergent herbicides are proactive, creating a chemical barrier just below the soil surface. This barrier inhibits cell division in weed seeds, preventing them from establishing a root system after germination. To be effective, this type of herbicide must be applied before the weed seeds sprout.
Post-emergent herbicides are reactive, designed to control weeds that are already visible and actively growing above ground. These systemic chemicals are absorbed through the weed’s foliage and travel down to the root system to kill the entire plant. Therefore, the choice of product and the application schedule depend entirely on whether the goal is to prevent new weeds or to eliminate existing ones.
The Critical Spring Application Window
The most crucial application window occurs in early spring, and the timing is determined by soil temperature, not air temperature. The target for applying a pre-emergent weed and feed is when the soil temperature consistently reaches 50 to 55 degrees Fahrenheit, measured at a depth of one to two inches. This specific range signals that summer annual weeds, particularly crabgrass, are beginning to germinate.
Applying the product too early means the herbicide will break down before the weeds begin to germinate, as most pre-emergents are effective for only eight to twelve weeks. A visual indicator in many regions is the blooming of the forsythia shrub, which often coincides with the optimal 50-degree soil temperature.
If the spring application includes a post-emergent herbicide, apply it when weeds are actively growing, but daytime temperatures remain below 90 degrees Fahrenheit to prevent damage to the lawn. Post-emergent effectiveness relies on the weed absorbing the chemical through its leaves while actively metabolizing. Delaying application until the hottest part of summer can stress the grass, potentially leading to scorching.
Fall Application for Lawn Recovery
The second significant application window occurs in late summer or early fall. Fall application is primarily focused on the “feed” component, often called winterizing, to help the lawn recover from summer stress. The fertilizer encourages the grass to develop a deep, robust root system and store carbohydrates for winter dormancy, leading to a quicker and thicker green-up the following spring.
If the fall product contains a post-emergent weed killer, its timing is highly effective. Broadleaf weeds like dandelions are beginning to pull nutrients down into their roots in preparation for winter. The herbicide is carried along with these stored nutrients, killing the entire plant more thoroughly than a spring application might. Apply fall weed and feed when soil temperatures are between 55 and 60 degrees Fahrenheit.
A fall pre-emergent application targets winter annual weeds, such as annual bluegrass, that germinate as the soil cools down. This preventive treatment should be applied when the soil temperature drops to approximately 70 degrees Fahrenheit. Complete any fall application before the first hard frost, which signals the end of active growth for most weeds and grasses.
Applying Weed and Feed: Essential Conditions and Follow-Up
Regardless of the season, the physical conditions during application are critical for the product to work as intended. Granular weed and feed products containing post-emergent herbicides must be applied to damp grass. This ensures the herbicide granules stick to the leaves of the weeds, allowing the chemical to be absorbed and transported systemically to the roots.
It is necessary to wait 24 to 48 hours after application before watering the lawn or expecting rain. Watering too soon washes the herbicide off the weed leaves before it can be absorbed, rendering the treatment ineffective.
Avoid mowing the lawn for one to two days before application and for at least 24 hours afterward. This waiting period allows the weeds to have maximum leaf surface area to intercept the granules and gives the systemic herbicide sufficient time to move throughout the plant tissue.
To protect local waterways, immediately sweep any product that lands on sidewalks or driveways back onto the lawn. This simple step prevents the chemicals and nutrients from being washed away in a storm and contributing to runoff.