Weed and feed products combine fertilizer to nourish turf with herbicide to control unwanted plants. Precise application timing is essential; using the product incorrectly in a climate like Iowa can render the chemicals ineffective or damage the lawn. Correct timing ensures the fertilizer benefits the grass during peak growth and the herbicide targets weeds when they are most vulnerable. Success depends on monitoring biological signals from the soil and weeds, rather than relying solely on calendar dates.
Understanding Weed and Feed and Iowa’s Grass
Iowa lawns primarily consist of cool-season grasses, such as Kentucky Bluegrass and Fescues, which thrive in cooler temperatures. These grasses have two periods of vigorous growth: spring and fall, often struggling or going dormant during mid-summer heat. Understanding this cycle is fundamental to maximizing the benefits of weed and feed.
The product’s “weed” portion contains two types of herbicides. Pre-emergent herbicides create a chemical barrier in the soil, preventing weed seeds like crabgrass from germinating. Post-emergent herbicides kill weeds that are already actively growing and visible. The fertilizer component, a blend of nitrogen, phosphorus, and potassium, provides essential nutrients. Since these components require specific environmental conditions, a single application must be timed carefully to align with all requirements.
Critical Timing for Spring Application
The spring application window is dictated by the germination of crabgrass, Iowa’s most common summer annual weed. Crabgrass seeds sprout when the soil temperature consistently reaches 50 to 55 degrees Fahrenheit, measured at a depth of two to four inches. This temperature range triggers the need for a spring weed and feed product containing a pre-emergent herbicide. While this typically occurs from mid-April to early May in central Iowa, monitoring soil temperature is more accurate than using calendar dates.
Applying the pre-emergent barrier too early risks the chemical degrading before the seeds sprout, leaving the lawn unprotected. Applying it too late means the crabgrass has already germinated, rendering the pre-emergent useless. For the post-emergent component to control existing broadleaf weeds, the air temperature should be between 60°F and 85°F, and weeds must be actively growing. The product granules must stick to the moist foliage for chemical absorption, often requiring a light dew or brief wetting before application.
Late Season and Fall Application
The second application opportunity is in the late season, from late September to early November, focusing primarily on perennial broadleaf weeds. This timing is effective because perennial weeds, such as dandelions and clover, are moving carbohydrates to their roots for winter storage. When a post-emergent herbicide is applied, the weed transports the chemical directly into its root system, resulting in a more complete kill.
The fall application also strengthens cool-season grass for winter dormancy. The fertilizer component should contain a higher nitrogen concentration, encouraging deep root growth and food storage rather than excessive top growth. This process enhances the lawn’s ability to withstand winter and leads to an earlier green-up in the spring. The fall treatment focuses on eliminating established perennial weeds and bolstering root health, rather than pre-emergent control.
Preparing and Applying Weed and Feed Safely
Preparation and Spreading
Proper preparation ensures the product works as intended and is distributed uniformly. Before application, mow the lawn to its normal height two to four days in advance. This provides enough leaf surface for the herbicide to adhere without immediately removing the product. Granular products must be spread using a rotary or drop spreader. Ensure the spreader setting matches the product label to prevent over-application, which can burn the grass. Fill the spreader on a driveway or sidewalk, away from the grass, to contain spills and prevent concentrated damage.
Post-Application Care
Application should occur when weed foliage is damp, ideally from a morning dew, so the herbicide granules stick to the leaves. After spreading, do not mow the treated area for at least 24 to 48 hours to allow sufficient time for the herbicide to be absorbed. Watering should also be delayed for 24 hours to give the post-emergent chemical time to work. After this delay, watering may be required to activate the fertilizer and any pre-emergent component. Finally, sweep any granules that land on hard surfaces back onto the lawn immediately to prevent runoff into storm drains and local waterways.