“Weed and feed” is a product designed to address two lawn care needs simultaneously: nourishing the grass and controlling weeds. This convenience product combines a fertilizer, which supplies nutrients like nitrogen, phosphorus, and potassium, with a weed killer, or herbicide. The challenge in South Carolina lies in timing the application precisely. Applying fertilizer while the lawn is dormant can encourage weed growth, while applying the herbicide component at the wrong time renders it useless. Success depends entirely on matching the application to the needs of the lawn and the life cycle of the weeds.
Pre-Emergent Application Based on Soil Temperature
The most time-sensitive component of a weed and feed product is the pre-emergent herbicide, which creates a chemical barrier in the soil to stop weed seeds from sprouting. For this barrier to be effective against summer weeds like crabgrass, the application must be completed before the weed seeds begin to germinate. This germination period is not determined by the calendar but by the temperature of the soil itself.
The critical window for crabgrass prevention opens when the soil temperature, measured at a depth of two to four inches, reaches 50 to 55 degrees Fahrenheit. Applying the pre-emergent after the soil has warmed past this point means the weed seeds have already begun to sprout. In South Carolina, this soil temperature threshold varies significantly across the state’s distinct climate zones.
The timing varies significantly across South Carolina’s climate zones:
- Coastal and Lowcountry regions (Charleston, Hilton Head) experience the earliest warming, with the window opening mid-January to mid-February.
- The Midlands (Columbia, Aiken) window is slightly later, typically between February 1st and February 20th.
- The Upstate and Mountain regions (Greenville, Spartanburg) have the latest window, often beginning around February 10th and extending toward the end of the month.
Tracking local soil temperatures online or using a soil thermometer is the most reliable method for pinpointing the exact time to apply the preventive herbicide.
Fertilization and Post-Emergent Timing for SC Grass Types
The second function involves fertilizing the existing turf and controlling broadleaf weeds that have already sprouted (post-emergent control). Timing is dictated by the active growth phase of the specific grass type for nutrient absorption. Most South Carolina lawns use warm-season grasses like Bermuda, Zoysia, and Centipede, which thrive in the heat.
For warm-season lawns, fertilizer should only be applied once the grass has fully broken dormancy and is actively greening up. This typically occurs when soil temperatures reach 65 degrees Fahrenheit, pushing the first feeding window into late April or early May. Applying fertilizer earlier risks feeding the weeds and potentially damaging the still-dormant turf.
The post-emergent herbicide targets visible weeds like dandelions and clover. It works best when the target weeds are young and actively growing, with daytime air temperatures ideally between 65 and 85 degrees Fahrenheit. This aligns well with the late spring and early summer feeding schedule for warm-season grass.
Tall Fescue is a cool-season grass common in the Upstate that grows best in lower temperatures. Fescue should primarily be fed in the cooler periods of early spring and, more importantly, in the fall (September or October). Applying a combined weed and feed product to fescue during the summer heat can cause stress and damage.
Finalizing Application: Weather and Safety Considerations
Once the correct seasonal window is determined, the application relies on immediate environmental conditions. Granular weed and feed products require contact with the weed’s foliage to be effective. Therefore, the lawn must be slightly moist from dew or a light sprinkling to ensure the granules adhere to the broadleaf weed surfaces.
The application should be followed by a period without rain (ideally 24 to 48 hours) to allow the herbicide to be absorbed by the weeds. Avoid applying the product before a heavy downpour, as this washes away granules, reducing efficacy and potentially leading to runoff. Wind is another factor to monitor, as strong breezes can cause the granular product to drift, leading to uneven coverage or damage to adjacent plants.
The lawn should be mowed two to three days before applying the product to ensure weed leaves are exposed and large enough to catch the granules. After application, avoid mowing for a couple of days, giving the herbicide adequate time to work. Most combination products are designed for a maximum of two applications per year, and homeowners must always follow the manufacturer’s label for safety and frequency.