Weed and Feed is a combination product, merging a granular fertilizer with an herbicide, designed to kill existing weeds and strengthen the turf simultaneously. The fertilizer component supplies nutrients like nitrogen, phosphorus, and potassium to promote healthy grass growth, while the herbicide targets unwanted plants. Successful application depends entirely on precise timing, which varies significantly based on geographic location and grass type. In Tennessee, applying this product at the wrong time can damage the lawn and waste the product’s effectiveness.
Understanding Weed and Feed in the Tennessee Context
Tennessee is situated in the “transition zone,” a challenging climatic area where summers are often too hot for cool-season grasses and winters are too cold for warm-season varieties. Lawns across the state commonly contain either cool-season grasses, such as Tall Fescue, or warm-season grasses, like Bermuda and Zoysia. The specific grass type dictates its active growing season, which determines the optimal window for applying fertilizer.
The herbicide component can be pre-emergent, post-emergent, or both. Pre-emergent herbicides form a chemical barrier in the soil to prevent weed seeds from sprouting. Post-emergent herbicides are absorbed through the leaves of existing weeds to kill them. Since fertilizer is applied when grass is actively growing and herbicides are timed to weed life cycles, the combination product requires careful timing to work effectively without harming the lawn.
Spring Timing: Targeting Pre-Emergent Weeds
The most important application window for a pre-emergent Weed and Feed product is in early spring, before summer annual weeds like crabgrass begin to germinate. Timing is based not on the calendar date, but on consistent soil temperature. Crabgrass seeds germinate when the soil temperature consistently reaches 55 degrees Fahrenheit at a two- to three-inch depth for four consecutive days.
The application must occur just before this threshold is reached to establish the preventative barrier. This window typically opens in late February or early March in West Tennessee and closer to mid-March or early April in East Tennessee. Homeowners can track this using online soil temperature maps provided by extension offices. A visual indicator is when the forsythia shrub is in full bloom, which often correlates with the target soil temperature range.
Applying a pre-emergent too late means crabgrass has already sprouted, rendering the product less effective since it does not kill existing growth. If the product contains a post-emergent component, it must be timed to a damp lawn so the granular herbicide sticks to and is absorbed by young weeds. The goal of this spring application is to prevent summer weed infestation while giving the turf nutrients as it breaks dormancy.
Fall Timing: Addressing Post-Emergent and Cool-Season Weeds
The second crucial time for a Weed and Feed application occurs in the fall, generally from September through November. This period is important for applying post-emergent herbicides to broadleaf weeds, such as clover and dandelion, which are actively absorbing nutrients for winter dormancy. Applying a post-emergent product now ensures the herbicide is transported down to the weed’s root system, resulting in a more complete kill.
Fall timing is also essential for cool-season grasses like Fescue, as the fertilizer component strengthens the root system before winter. This late-season feeding promotes root development and nutrient storage, aiding in winter survival and ensuring a quicker green-up the following spring. Warm-season grasses like Bermuda and Zoysia should not be heavily fertilized late in the fall, as feeding them too close to the first frost encourages vulnerable new growth.
To prevent winter annual weeds like Poa annua, a second pre-emergent application may be needed when soil temperatures drop below 70 degrees Fahrenheit, typically in September or early October. This application prevents germination throughout the cooler months, stopping these weeds from becoming established. The fall treatment is strategically designed to prepare the lawn for the next growing season by eliminating competition and fortifying the turf.
Application Guidelines and Post-Treatment Care
Successful application of a granular Weed and Feed product requires attention to the lawn’s moisture level. For products containing a post-emergent herbicide, the grass blades need to be lightly damp when applied so the granules stick to the weed foliage. This contact ensures the weed killer is absorbed effectively.
After application, it is necessary to wait at least 24 to 48 hours before watering the lawn or allowing significant rainfall. This waiting period allows the herbicide component time to be absorbed by the weeds before being washed off. For pre-emergent products, however, a half-inch of water or rain is needed within a few days of application to activate the chemical barrier in the soil.
Homeowners should observe the product label’s instructions regarding mowing, which often recommend waiting a couple of days after treatment. Mowing too soon can remove the herbicide from the weed leaves before it has fully worked, reducing the product’s effectiveness. Avoid applying the product just before a heavy rain is forecast, as this could wash the granules away before they adhere to the weeds or are absorbed into the soil.