The Best Grass Seeds to Plant With Existing Grass & Weed Killer

Overseeding With Herbicides

• Preemergent herbicides often are applied in the spring, before the soil temperature reaches about 58 degrees Fahrenheit, to prevent crabgrass (Digitaria ischaemum and Digitaria sanguinalis) and other annual weed seeds from growing. They sometimes are applied in the fall to control cool-season annuals, which also is the best time to sow grass to fill in bare spots on lawns. Most herbicides designed to prevent weed seeds from germinating also will kill grass seeds, and should not be applied before overseeding. Depending on the chemical, it can be between 6 weeks and 4 months before the lawn is safe for overseeding. However, the chemical siduron, also known as tupersan, can be safe for turfgrass seedlings. Check product labels for specific information.

Best Cool-Season Grasses

• The best grass seed for cool-season lawns often is a mix of different varieties. Fescues (Festuca spp.) grow well in shady locations. They can be mixed with Kentucky bluegrass (Poa pratensis), which often is considered the best all-around turf grass. All these grasses are hardy in U.S. Department of Agriculture plant hardiness zones 2 through 7. To increase the traffic resistance of cool-season lawns, bluegrass mixes often include perennial ryegrass (Lolium perenne), which is hardy in the same zones. For most herbicides, wait 1 to 4 months after application to plant seed. Herbicides containing mesotrione or quinclorac and carfentrazone, however, can be used on seedling cool-season lawns seven days after the seeds germinate.

Best Warm-Season Grasses

• Warm-season grasses are grown from seed less often than cool-season grasses, and rarely are sold as mixed seed. They can be sown about 4 months after using a preemergent herbicide or 1 month after using a different product to control lawn weeds. The best variety to plant will depend on lawn conditions. Certain varieties of Bermudagrass (Cynodon spp) and Bahiagrass (Paspalum notatum), hardy in zones 7 through 10, are grown from seed. Bemudagrass has thick green growth and is considered one of the best grasses for full sun. Bahia grass has a coarse texture, but it will grow well in poor soil. Centipedegrass (Eremochloa ophiuroides), hardy in zones 7 through 8, also can be grown from seed. It is low-maintenance and will tolerate some shade.

Winter Ryegrass

• Overseeding a warm-season lawn, such as Bermudagrass, can refer to planting ryegrass for the winter as well as to filling in bare spots on lawns. Warm-season grasses go dormant and turn brown in the winter, and planting ryegrass over the lawn will provide winter color. For this, perennial ryegrass is grown as an annual or annual ryegrass (Lolium multiflorum) is planted. Ryegrass seeds should be planted about 30 days before the first frost date in the area, and herbicides should not be applied before seeding. If a preemergent herbicide is on the lawn, the ryegrass will not germinate.