Weed-and-feed products combine fertilizer and herbicides to do two jobs at once. But their promised labor savings can backfire if the recommended time for weed control doesn’t coincide with the best time and rates for fertilizing. Most also pose an herbicide-overdose risk when used for follow-up fertilizing. Corn gluten with added organic fertilizer is the safest weed-and-feed.
If you use a herbicide, choose one that’s labeled as safe for the type of turf you’re growing and effective against the weeds you’ve got. The label states when and in which conditions to use the product. Some herbicides work only within a certain temperature range; others work only when applied at a specific time of year.
Postemergence herbicides kill existing weeds that are actively growing. These come in two basic forms: contact and systemic. Contact herbicides kill only the part of the plant they touch. Most act quickly and work best against annual weeds. Systemic herbicides circulate inside the plant, killing the whole thing. They’re more effective than contact herbicides on perennial weeds, though repeat treatments might be needed.
Hand-weeding is still the best defense on small lawns where the number of weeds isn’t overwhelming. It’s most effective against annual broadleaf weeds. Pulling them while they’re young—before they flower and seed—is the simplest way to prevent them from spreading.
Once the weed and roots are out, smooth the soil, work in some compost, and patch the area with lawn seed. Keep the soil evenly moist until the grass is 1 inch high.
Learn how to kill weeds in your lawn without killing your grass.
When using any postemergence herbicide, don’t apply them over your entire lawn, if possible. Instead, spot-treat isolated weeds or weedy patches.
Other ways to gauge application time include using bioindicators, such as plants whose growth signals the correct time for application. For instance, in northern climates, spring Crabgrass applications are often timed when Forsythia is blooming, which frequently (but not always) occurs when soil temperatures are in the 50°F range. Another option is to time applications based on the calendar. For example, if you typically apply a pre-emergent herbicide in mid-April with success, then continue that routine.
Post-Emergent Herbicide: Kills weeds that are actively-growing and have already emerged from soil. It’s an ideal herbicide for spot-treating lone offenders but is often applied to entire lawns. Post-emergent herbicides come in two basic forms – contact and systemic.
Perennial Weed: Lives for two or more years; plants grow as long as conditions are favorable and frequently die back to soil level with hard frost; new growth emerges at the start of the growing season, originating from roots or stem remains; in warmer regions, some perennial weeds can be green year-round.
Examples: Bermudagrass, Crabgrass, Giant Foxtail, Goosegrass, Quack Grass
If you have a yard, you have weeds. They may lurk in the lawn, thrive under a shrub or flourish in flowerbeds, making weed control a constant battle. It requires patience, persistence and knowledge – of both types of weeds and the weapons you have to eradicate them.
Weed seed germination occurs when soil reaches the correct temperature. The best way to determine the ideal time to apply pre-emergents is to contact your local Cooperative Extension System office or master gardeners, who have access to regional soil temperature data.