When homeowners look to improve the appearance of their lawns, the combined product known as “Weed and Feed” often comes up as a convenient solution to address two problems at once. These combination treatments are not designed for seeding or starting a new lawn from scratch; instead, they are formulated specifically for the strengthening and maintenance of an already established turf. The product’s success lies in its ability to simultaneously nourish the existing grass while eliminating competitive weeds.
Defining the Dual Action Product
“Weed and Feed” integrates two distinct chemical functions into a single granular or liquid application. The “Feed” portion is a standard lawn fertilizer, providing necessary nutrients for grass health and growth. The “Weed” component is a selective herbicide, designed to kill unwanted plants without damaging the desired turfgrass. This dual formulation allows for a single pass across the lawn rather than two separate treatments.
The combination of fertilizer and herbicide means these products are incompatible with new seeding projects. The herbicide component, particularly the pre-emergent type, functions by preventing seeds from successfully germinating. Applying Weed and Feed to a newly seeded area will likely prevent the new grass seeds from sprouting. Therefore, this product is best applied to mature, established turf that only requires maintenance and weed control.
How the Fertilizer Component Boosts Existing Grass
The “Feed” aspect supplies the lawn with macronutrients that promote robust growth and improved appearance. Lawn fertilizers rely on a specific ratio of three elements, known as NPK: Nitrogen (N), Phosphorus (P), and Potassium (K).
Nitrogen is the primary driver for leaf growth and the deep green color homeowners seek. It is integrated into the chlorophyll molecule, which allows the grass blades to efficiently perform photosynthesis. Phosphorus supports cell division and energy transfer, which is important for strong root development.
A deep, extensive root system allows the grass to absorb water and nutrients more effectively, making the turf more resilient to environmental stresses like drought. Potassium regulates internal plant processes, helping the grass manage water balance by regulating the opening and closing of tiny pores on the leaves called stomata.
By delivering these nutrients, Weed and Feed promotes density and vigor in the existing turf, causing the individual grass plants to thicken and spread. A dense, healthy lawn naturally outcompetes weeds for sunlight, water, and soil nutrients. This mechanism creates a natural barrier to future weed growth.
The Specifics of Herbicide Action and Timing
The “Weed” portion of the product contains selective herbicides that target broadleaf weeds, such as dandelions and clover, while leaving the narrow-leafed turfgrass unharmed. This selectivity works because turfgrasses are monocots, while most common lawn weeds are dicots, and the herbicide is formulated to disrupt the growth processes unique to dicot plants. The herbicide component can be either a pre-emergent or a post-emergent type, and understanding the difference is paramount for effective use.
A pre-emergent herbicide is applied before weed seeds sprout, creating a chemical barrier near the soil surface that prevents the seeds from developing roots and shoots. This type is timed best for early spring to stop summer annuals like crabgrass, or in the fall to control winter annuals. In contrast, a post-emergent herbicide is used to eliminate weeds that are already visible and actively growing.
For post-emergent Weed and Feed products to work effectively, they must be applied when the weeds are actively growing, often when temperatures are between 50°F and 75°F. The granules must stick to the leaves of the target weeds, where the chemical is absorbed and moves systemically throughout the plant to kill it. The lawn should be moist before application so the granular particles adhere properly to the weed foliage. Improper timing, such as applying during a drought or when weeds are dormant, will significantly reduce the herbicide’s effectiveness.