How long you must wait to plant grass seed after treating your lawn with a Scotts Weed B Gon product depends on which product you use. When fighting broadleaf weeds such as dandelions with the basic Weed B Gon weed killer, wait at least three weeks to sow your grass seed. This product specifically targets the seeds of broadleaf weeds, but it can stop or slow down your grass seed’s germination as well.
When fighting grassy weeds, you must wait a little longer to plant your grass seed, whether you’re seeding your entire lawn, overseeding or treating bare patches. With the Weed B Gone Plus Crabgrass Control, wait at least four weeks to plant seed. Because this is specially formulated to stop grassy weed seeds from germinating, it also can stop your regular grass seed from growing.
Without Crabgrass Preventer
Keeping your lawn weed-free is a constant battle that uses cultural practices, such as deep waterings, to encourage grass to choke out weeds, as well as chemical products, such as using Weed B Gon, to kill weeds before they start. These chemicals often kill grass seed as well, keeping it from germinating along with the weed seeds, so wait before you sow your seed.
Although you can’t spread grass seed at the same time you spray your lawn with Weed B Gon, other options exist to treat your lawn for weeds at the same time you plant seed. These typically come in the form of weed and feed products that offer fertilizer along with the herbicide. Look for products specifically designed to be spread with grass seed, often noted on the label as a starter fertilizer plus weed control.
When you’ve already planted your grass seed and want to apply a pre-emergent herbicide to keep weeds from competing with your new grass for water and nutrients, have a little patience. Applying a weed-control product such as Weed B Gon too soon can kill young grass. Instead, wait until you’ve mowed the new grass at least three times before using herbicides on your lawn.
Most granular preemergence herbicides should be watered in with about ½ inch of irrigation water immediately following application. This activates the herbicide, which is absorbed by the young roots of weeds as they begin to grow.
In the spring, preemergence herbicides should be applied when air temperatures reach 65 to 70 °F for four consecutive days. On average, this is March 15-30 for the piedmont and mountains. In the fall, to control winter annuals, apply preemergence herbicides when nighttime lows reach 55 to 60 °F for four consecutive days. On average, this is September 1 to 15 for the piedmont and mountains.
Annual vs. Perennial: Annuals germinate, grow, and die within a twelve month period. Summer annuals, such as goosegrass, germinate in the spring, grow through the summer, set seed, and die at the onset of cold weather. Winter annuals, such as chickweed, germinate in the fall, grow through the winter, set seed, and die as temperatures rise in early summer.
Control with Herbicides
Weed control begins with proper management practices, which encourage a dense, healthy turf. A healthy turf shades the soil so that less sunlight reaches the ready to germinate weed seeds. A thick turf also minimizes the space available for weeds to become established.
Perennials grow for two or more years. They reproduce from vegetative parts such as tubers, bulbs, rhizomes, or stolons, though some also produce seed. Examples are dallisgrass, wild garlic, and clover.
Fertilize and lime at the proper time and according to a soil test. Proper lime application will help to maintain a soil pH where nutrients are readily available to the turf. In general, spring nitrogen fertilization should cease in March.
Proper management practices include mowing, watering, fertilizing, and liming. These are mentioned briefly here but are covered in detail in corresponding HGIC fact sheets. See HGIC 1205, Mowing Lawns, HGIC 1207, Watering Lawns, and HGIC 1201, Fertilizing Lawns.