Ignoring Recommended Seeding Rates Don't overdo it or cut corners. Too much grass seed causes undue competition for resources such as light, water, and nutrients, and grass seedlings struggle as a result. With fewer germinating weed seeds and mild, reliable temperatures, you may want to plant your new lawn in early fall. However, when planning your seed spreading strategy, it's important to keep in mind that using too much grass seed doesn't create a lush lawn.
In fact, your lawn really has a hard time and can fail completely with an excess of grass seed in the top layer of soil. The first question here is, how much beyond 10 pounds per 1,500 square feet? Anything up to 15 is fine. Anything up to 20 or a little more I doubt you'll have too much trouble. Problems can appear with any planting rate (I have had wet fungi when planting 1 seed per square inch for annual propagation), but the risks increase dramatically as the number of seeds per square inch increases.
Without a doubt, it is possible to put too much grass seed. Not only is using too many seeds wasteful, but it also provides more competition for the nutrients and water that seedlings need to grow. Excessive use of grass seed will likely cause a decrease in germination rate. It depends on how loose the earth is.
Grass seeds aren't strong enough to grow through the ground. They are designed to be placed on loose, prepared soil. Germination can quickly suffer from too much soil above them. After sowing lawn seeds, they will need constant and frequent watering, as opposed to “deep and less frequent watering” for mature lawns.
For aftercare, whether you've planted a new lawn or filled in an empty spot, start mowing the lawn after 8 weeks or until the lawn has reached a mowing height.