A crabgrass preventer, formally known as a pre-emergent herbicide, stops the germination of crabgrass seeds before they establish in your lawn. This herbicide does not kill existing weeds but creates a chemical barrier in the uppermost layer of the soil. When a crabgrass seed begins to sprout, it absorbs the chemical, inhibiting root growth and causing the seedling to die before it breaks the soil surface. Successful use depends on precise timing and accurate application to establish a uniform and effective barrier.
Understanding Optimal Application Timing
The success of crabgrass preventer hinges on applying the material before seeds germinate, which is tied directly to soil temperature. Seeds require the soil temperature at a depth of one to two inches to consistently reach 55 degrees Fahrenheit for several consecutive days. Applying the product too early risks the barrier breaking down, while applying it too late means the crabgrass has already sprouted. Regional climate differences dictate the precise application window. Monitoring local soil temperatures provides the most accurate timing, but a traditional sign is when the forsythia bushes in your area are blooming yellow.
Preparing the Lawn and Equipment
Before spreading the granular material, the lawn must be prepped to ensure the herbicide reaches the soil surface uniformly. Mow the turf to its normal spring height, and remove all debris, such as leaves or sticks. The lawn surface should be dry, allowing the particles to settle directly onto the soil for later water activation. The most precise step involves calibrating the spreader according to the specific product label instructions. Errors in setting the flow rate can lead to patchiness from under-application or turf damage from over-application. Proper calibration ensures the material is distributed at the exact rate required to form a consistent, protective chemical layer.
Step-by-Step Application Technique
The physical act of spreading the crabgrass preventer requires a systematic approach to guarantee even coverage and prevent missed areas. It is recommended to use the half-rate method, which involves setting the spreader to half the recommended rate and making two passes over the entire lawn. The first pass should be completed in one direction, such as north to south. The second pass should then be made perpendicular to the first, ensuring thorough cross-hatch coverage. This crisscross pattern minimizes the risk of streaking or gaps that can occur with a single pass.
When operating the spreader, begin walking before opening the hopper and close it before stopping to prevent a clump of material from dropping and potentially burning the turf. When maneuvering near hardscapes, ensure the spreader is turned off or angled inward to avoid broadcasting the product onto non-turf areas. Pay special attention to the perimeter of the lawn, as these areas retain heat and often see earlier crabgrass germination. Sweep any granules that land on hard surfaces back onto the lawn to prevent runoff and localized staining.
Post-Application Care and Watering Schedule
Immediately following application, the granular product must be activated to create the chemical barrier. Activation requires water to dissolve the granules and move the herbicide into the top layer of the soil. Generally, about 0.5 inches of water via irrigation or rainfall is necessary within a few days of application. If rainfall is not forecasted, use a sprinkler system to activate the product. Waiting too long allows the product to sit on the surface, susceptible to breakdown from sunlight. Limit foot traffic for 24 to 48 hours after watering in, and delay mowing for a few days to avoid disturbing the newly established barrier.
Avoiding Common Preventer Errors
A frequent mistake is applying crabgrass preventer on newly seeded turf areas, which can severely hinder the establishment of desirable grass seed. The herbicide’s non-selective action prevents both the crabgrass and the new grass seed from sprouting. If you plan to overseed in the spring, choose a specialized pre-emergent herbicide safe for new grass seedlings, or delay seeding until the fall.
Another common pitfall is applying the product too soon before or after core aeration or extensive dethatching. These processes physically disrupt the soil, breaking the continuous chemical barrier created by the herbicide. Any disturbance that exposes soil below the established barrier allows crabgrass seeds to germinate safely outside the herbicide’s reach.
Furthermore, crabgrass preventer will not kill existing, visible crabgrass plants. The product is strictly preventative, meaning it must be applied before the weed emerges; once a plant has sprouted, a different, post-emergent herbicide is required for control.