Answer: I strongly suggest you start all over. Success or failure of a home lawn is closely tied into how well the soil and site was prepared prior to lawn establishment. Eliminating weed problems existing on the site is an important first step. Perennial weeds, such as quackgrass, need to be controlled prior to lawn seeding or sodding. Weed control options include digging by hand or using a translocated (moves within plant) nonselective herbicide, such as glyphosate, sold as Roundup and other trade names. Glufosinate ammonium (Finale) does not translocate, so may only provide limited control of perennial weeds. Both herbicides don't leave active soil residues that would harm lawn seedlings. Read, understand, and follow all label directions.
Before seeding or sodding, it's very important to thoroughly work the soil (by rotary tiller). Amend poor soils, such as heavy clay, by adding organic matter. Sources include compost, rotted manure, peat, and quality topsoil. Incorporate these materials into the existing soil, rather than layering them on the surface. Six inches or more of organic matter, tilled to a depth of about 8" will greatly improve your soil.
Starter fertilizers may also be mixed into the soil surface prior to lawn establishment. Starter fertilizers typically have balanced ratios of nitrogen, phosphorus, and potassium (N, P, K), such as 10-10-10 or 12-12-12. Soil test results may reveal a shortage of phosphorus or potassium, which would influence the decision of how much starter fertilizer is needed.
When preparing the soil, it's important to establish a favorable final grade. Rough grading should include removal of any rock or other debris. Avoid burying construction debris, as this could cause problems for the grass later. Eliminate any depressions or raised areas. Final slopes should be 1 to 2 percent away from buildings (1 to 2 feet drop per 100 feet of run) to assure good surface drainage.
Taking shortcuts in soil and site preparation often leads to assorted lawn problems later. If you take the time and effort to do a thorough job before seeding or sodding, you will be rewarded for years to come with a thick, healthy lawn.
Once the soil has been prepared, broadcast your seed and cover it lightly with a thin layer of peatmoss to help keep the seedbed moist. Grass seeds should germinate in 7-10 days. Keep it well watered so the grass grows thick enough to crowd out weeds.
Best wishes with your new lawn!
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