“Weed and feed” refers to lawn care products that combine fertilizing the grass and killing weeds into a single application. While these products offer a convenient, all-in-one solution, their dual chemical nature raises safety questions. The risk depends heavily on the specific chemical formulation, the application method, and the level of exposure experienced by people, pets, and the environment.
Understanding the Active Components
The composition of these combined products consists of two distinct functional groups. The “feed” portion is a standard fertilizer, typically containing nutrients like nitrogen, phosphorus, and potassium (NPK) to promote rapid grass growth. These components are absorbed by the turf to enhance its color and density.
The “weed” portion contains selective herbicides designed to kill broadleaf weeds without harming the grass. Common active ingredients include 2,4-D, MCPP (mecoprop), and dicamba. Product toxicity varies significantly because each herbicide is formulated in different chemical forms, such as salts or esters, which affects its behavior in the environment and the body.
Direct Health Risks to People and Pets
Exposure to the active chemicals can occur through dermal contact, inhalation, or accidental ingestion. Children face a higher risk because they spend more time playing on treated lawns and engage in hand-to-mouth behaviors, leading to greater intake relative to their smaller body weight. Herbicides tracked indoors can also persist in house dust, prolonging human exposure.
Dogs are often more sensitive to certain herbicides, such as 2,4-D, due to their reduced ability to metabolize and excrete the chemical. Studies suggest a potential association between exposure to lawn chemicals and an increased risk of canine malignant lymphoma. Acute poisoning from ingesting granules can result in severe symptoms, including vomiting, diarrhea, drooling, or neurological effects like convulsions.
Manufacturers establish a re-entry interval, which is the time people and pets must stay off the treated area. This interval typically ranges from 24 to 72 hours, or until the product has completely dried and been watered into the soil. Adherence to this waiting period minimizes the chance of residues transferring to skin, paws, or being accidentally ingested.
Environmental Impact and Non-Target Organisms
Applying combined products across an entire lawn leads to the overuse of herbicides, as the chemical is spread even where no weeds are present. This non-targeted application introduces unnecessary chemicals into the ecosystem, affecting soil health. Repeated use of synthetic fertilizers and herbicides can negatively impact beneficial microorganisms, fungi, and earthworms vital for maintaining healthy soil structure.
Runoff from rainfall or over-irrigation can carry both fertilizer and herbicide components into local waterways through storm drains. Excess nitrogen and phosphorus act as pollutants, leading to eutrophication. This process causes rapid algae growth, which depletes oxygen and harms aquatic life.
The herbicide component poses a separate threat, as compounds like 2,4-D are frequently detected in streams and shallow groundwater sources. Granular products can be mistaken for food by birds, leading to direct toxicity. Broadleaf weed killers can also drift or accumulate on plants, presenting a danger to non-target flora and pollinators such as bees and butterflies.
Minimizing Risks Through Safe Use
The most effective way to reduce risks is to follow the label instructions precisely. Applying the product at the correct rate avoids over-application, a common cause of health and environmental issues. Timing the application to avoid windy conditions prevents chemical drift onto neighboring properties or sensitive landscape plants.
After application, any granules on hard surfaces like driveways or sidewalks should be swept back onto the lawn to prevent them from washing into storm drains. Store unused product in its original container in a secure location, such as a locked shed, out of reach of children and pets.
A safer long-term approach is to separate the two functions: use fertilizer only when needed and spot-treat individual weeds with a targeted herbicide. Alternatively, switching to organic fertilizers and natural weed control methods, such as manual removal or horticultural vinegar, can nearly eliminate chemical exposure risks. This significantly reduces the product’s overall environmental impact.