A “weed and feed” product combines fertilizer, which supplies nutrients for grass growth, and an herbicide, which controls weeds. This dual-action product requires accurate timing, especially in Missouri’s challenging “transition zone” between northern and southern climates. Improper application can render the product ineffective against weeds or harm the grass if fertilizer is applied when the turf is stressed. The biological needs of the lawn and target weeds must align for the combined product to work as intended.
Understanding Missouri’s Lawn Types and Timing Goals
Missouri supports both cool-season and warm-season turfgrasses, which have different growth cycles that dictate application timing. Cool-season grasses, such as Tall Fescue and Kentucky Bluegrass, grow most vigorously in the spring and fall when temperatures are mild. Warm-season grasses, like Zoysia and Bermuda grass, thrive in the summer heat and enter dormancy when temperatures drop.
The “feed” component (fertilizer) is best applied during the grass’s active growth phase to support root and leaf growth. Applying fertilizer during a grass’s dormant or stressed period, such as to cool-season turf in summer heat, can cause significant damage.
The “weed” component includes two types of herbicides. Pre-emergent herbicides form a chemical barrier in the soil, stopping weed seeds from germinating, and are suitable for preventing annual weeds like crabgrass. Post-emergent herbicides are absorbed through the leaves of actively growing weeds, killing existing plants like dandelions and clover. Precise timing is required because the optimal periods for fertilizing, preventing germination, and killing existing weeds often do not coincide perfectly.
The Critical Spring Application Windows
The first major application window occurs in the spring and focuses primarily on pre-emergent weed control. This timing is crucial because pre-emergent herbicides must be in place before annual weed seeds begin to sprout, specifically targeting the prevention of summer annuals like crabgrass.
The most reliable indicator for this window is soil temperature, not the calendar date. Crabgrass begins to germinate when the soil temperature consistently reaches 55 degrees Fahrenheit at a depth of one to two inches. The pre-emergent product must be applied and activated just before this threshold, when soil temperatures are consistently between 50 and 55 degrees Fahrenheit for several consecutive days.
This period typically falls between mid-March and mid-April in central and southern Missouri, extending slightly later for northern areas. The product must be watered into the soil, either by rain or irrigation, to create the necessary chemical barrier. Applying the product too early risks the barrier breaking down, while applying it too late means the crabgrass has already begun to sprout, rendering the treatment ineffective.
If the pre-emergent window is missed, homeowners must switch to a post-emergent herbicide for visible weeds later in the spring. Post-emergent products are most effective when weeds are small and actively growing. Application should be avoided during high heat (above 85 degrees Fahrenheit) to prevent damage to the turfgrass. For cool-season grasses, it is often better to delay further fertilization until the cooler fall weather returns.
Late Summer and Fall Application Strategy
The second major application period occurs in late summer and fall, primarily benefiting Missouri’s cool-season grasses. The focus shifts from preventing annual weeds to controlling perennial broadleaf weeds and strengthening the lawn for winter. Perennial weeds, such as dandelions and clover, actively move carbohydrates down to their roots in the fall to prepare for winter dormancy.
Applying a post-emergent herbicide during this time allows the chemical to be transported deep into the weed’s root system along with the stored nutrients, resulting in a more effective kill. This window generally opens in September and extends through October, when evening temperatures begin to cool but before the first hard frost. Targeting established broadleaf weeds in the fall significantly reduces the population that would emerge the following spring.
The “feed” component focuses on “winterizing” the cool-season lawn. Fall fertilization promotes deep root development and the storage of energy reserves. This helps the grass withstand winter stress and allows it to green up earlier and more vigorously the following spring. For cool-season turf, applications around Labor Day and again in late October or early November, using a formula high in potassium and nitrogen, provide the best results for winter hardiness.