Spring lawn care often involves “weed and feed,” a combined product that nourishes turf and controls unwanted growth. This product combines essential nutrients (nitrogen, phosphorus, and potassium) with specific chemical herbicides. Applying this product at the correct time is crucial, as mistiming the application can render the herbicide ineffective or potentially damage the lawn. Precise timing ensures the fertilizer is available when the grass needs it most and the weed control chemicals target developing weeds before they become established.
Identifying the Ideal Application Window
The most reliable indicator for applying spring weed and feed is the sustained temperature of the soil, not a calendar date. Weeds like crabgrass (Digitaria spp.) germinate when the soil temperature consistently reaches 50 to 55 degrees Fahrenheit at a depth of two to three inches. The pre-emergent herbicide component must be applied before the weed seeds sprout, making this temperature range the primary target window.
The efficacy of the herbicide depends on creating a chemical barrier in the top layer of the soil before weed seed germination begins. If the product is applied too late, the pre-emergent chemical will fail to provide control. Conversely, applying the product too early, when soil temperatures are still below 50 degrees, risks the herbicide breaking down or leaching out of the soil. This leaves the lawn unprotected during the actual germination window later in the spring.
Since measuring soil temperature is uncommon, homeowners can use visual cues known as phenological indicators.
Phenological Indicators
One common sign is the state of the forsythia bush (Forsythia spp.). The ideal application window often coincides with the moment the bright yellow flowers start to drop their petals, indicating the soil is approaching the 50-degree threshold. Another reliable indicator is the budding of lilac bushes (Syringa vulgaris). These plant-based observations provide a localized way to gauge the necessary soil conditions, adapting the timing to specific climate conditions.
While early spring application targets grassy weeds like crabgrass, a separate timing consideration exists for broadleaf weeds like dandelions. If the product contains only post-emergent chemicals, application can be delayed until weeds are actively growing and temperatures are consistently above 60 degrees Fahrenheit. However, most spring “weed and feed” products prioritize pre-emergent action, making the 50 to 55-degree soil temperature the trigger for optimal timing.
Understanding Product Types and Grass Specifics
The “weed” component uses two primary types of herbicides, each requiring different timing. Pre-emergent herbicides interrupt cell division in the sprouting seed, forming a chemical barrier that stops the weed before it breaks the soil surface. This requires application before the 50-55 degree soil temperature trigger.
Post-emergent herbicides are absorbed through the leaves of actively growing weeds, disrupting their processes. These chemicals are applied when weeds are visible and often require moisture on the leaf surface to be effective. Most spring formulations prioritize pre-emergent action to control invasive crabgrass, which is easier to prevent than to kill once established.
The type of lawn grass modifies the ideal fertilizer timing, but the pre-emergent window is fixed by weed biology.
Grass Type Considerations
Cool-season grasses, such as fescue and bluegrass, begin active growth early in the spring. They benefit from the nutrient boost immediately following the pre-emergent application, aiding recovery from winter dormancy.
Warm-season grasses, including Bermuda and Zoysia, do not begin active growth until soil temperatures are consistently above 65 degrees Fahrenheit. Applying fertilizer too early is inefficient, as nutrients sit unused until the grass breaks dormancy. While the pre-emergent must be applied at the 50-55 degree mark, the fertilizer component for warm-season lawns is often better applied later in the spring or early summer.
Preparing for and Completing the Application
Before applying granular weed and feed, the lawn should be mowed to a normal height. Mowing should be avoided for several days immediately following application, as cutting too soon can remove the applied granules. The first practical step is consulting the product label to determine the appropriate setting for the broadcast or drop spreader.
Accurate spreader calibration is necessary to prevent under-application, which causes patchy control, and over-application, which can chemically burn the turfgrass. When applying, use the cross-hatch method: apply half the recommended rate in one direction (e.g., north to south), and the remaining half perpendicular to the first pass (e.g., east to west). This ensures uniform coverage and minimizes application stripes.
The post-application process is essential for activating the pre-emergent herbicide. Immediately after application, the lawn must be watered, either by irrigation or rain, to dissolve the granules and wash the active ingredient into the top layer of the soil. This watering creates the chemical barrier that prevents crabgrass seeds from sprouting.
If the product contains post-emergent chemicals for broadleaf weeds, a light dew or rain is often preferred, as the chemical needs to adhere to the leaf surface for absorption. Keep pets and children off the treated area until the granules have been completely watered into the soil and the grass blades are dry.