Do I Need to Weed Before Planting Grass Seed?

Weeds

• There are weed seeds in the soil waiting to germinate. These seeds use the starter fertilizer given to grass seeds and cause thinning turf. Weed seeds, such as crabgrass, wait for soil temperatures to rise in the spring to 60 degrees before germinating, according to Rhode Island State University. In addition, existing weeds take up important real estate in the soil causing undeveloped grass root systems. Removing weeds prevents future grass problems caused by grass competing with weeds.

Removing Weeds

• Use a broad-spectrum herbicide that kills all types of weeds such as grassy, broadleafed and sedge. Spray an herbicide containing glyphosate that does not leave residue in the soil that harms grass seeds. Glyphosate inhibits the weeds' ability to produce proteins. Within in 24 hours, the weeds dry out and die. First, water the lawn for two weeks to promote weed growth. Vigorously growing weeds are easier to kill than slowly growing weeds. Then spray the herbicide on the lawn.

When to Seed

• Wait five to 14 days before seeding the lawn after spraying the herbicide, as recommended by the University of Minnesota. The best time for seeding depends on the grass type you are trying to grow. Cool-season grass seed should be sown in the fall, and warm-season grass seeded in the spring. Avoid seeding the lawn in the summer. Grass seed must be moist to germinate. Hot summer conditions dry out the seed, preventing germination.

Seeding

• Seed the lawn in the morning when temperatures are cool and the ground is easier to keep moist. Applying a pre-emergent herbicide six weeks after seeding prevents weed seeds from germinating. Refrain from applying pre-emergent herbicide before seeding. The chemicals in pre-emergent herbicide can prevent your grass seed from germinating. Reapplying the pre-emergent herbicide in the fall or the following spring controls grassy and broadleaf seed germination.