A “weed and feed” product is a dual-action lawn care solution designed for homeowner convenience. It combines a granular fertilizer with a post-emergent herbicide, allowing a user to fertilize the turfgrass and simultaneously treat weeds in a single application. This combination is intended to promote a dense, healthy lawn while focusing its destructive power on a specific category of lawn invaders.
The Broadleaf Weeds Targeted
Standard weed and feed formulations are specifically engineered to eliminate broadleaf weeds, which are botanically classified as dicots. These plants are the primary targets because their cellular structure and growth patterns differ significantly from the monocotyledonous grasses that make up the lawn. The goal is to eradicate the weed without harming the desirable turf.
A wide variety of common lawn weeds fall into this susceptible broadleaf category. Homeowners frequently encounter and successfully treat persistent plants such as:
- Dandelions
- Clover
- Broadleaf plantain
- Common chickweed
- Henbit
- Dollarweed
- Creeping woodsorrel (also known as oxalis)
Since these products are post-emergent, they are designed to kill weeds that are already actively growing and visible above the soil line.
Mechanism of Killing
The selective killing action is achieved through the use of synthetic plant growth regulators, often called auxinic herbicides, such as 2,4-D. These chemicals are structurally similar to natural auxins, which are the hormones responsible for regulating plant growth and development. When a broadleaf weed absorbs the herbicide through its leaves, the chemical is translocated throughout the plant’s vascular system to its growing points, known as meristems.
The synthetic auxin overwhelms the plant’s natural hormone balance, causing an unsustainable rate of growth. This rapid, distorted growth, characterized by symptoms like stem curl-over and leaf twisting (epinasty), depletes the plant’s energy reserves. Ultimately, this excessive cellular activity leads to the systemic death of the weed.
Non-Target Casualties and Limitations
While effective against broadleaf weeds, the selective nature of the herbicide means there are significant limitations and risks to non-target plants. Standard weed and feed products generally do not control established grassy weeds, such as crabgrass, nutsedge, or common annual bluegrass. These weeds are botanically similar to the turfgrass itself, making it difficult for a selective herbicide to differentiate and kill them without also damaging the lawn.
The products are also ineffective against weed seeds that have not yet sprouted, as they lack the systemic action of pre-emergent herbicides. Furthermore, the herbicide component poses a risk of damage to desirable non-turf plants, including ornamental flowers, shrubs, and trees. If the granular product drifts or is applied over the root zone of these plants, the absorbed herbicide can cause growth distortions and lethal effects. Certain sensitive turf varieties, like St. Augustine or Centipede grass, may also be damaged if a product not specifically labeled for them is applied.