Can You Use Too Much Grass Seed?
With fewer germinating weed seeds and reliably mild temperatures, you may want to seed your new lawn in the early fall. As you plan your seed spreading strategy, however, it is important to note that using too much grass seed does not create a lusher lawn. In fact, your grass actually struggles and may fail completely with excessive grass seeds across the topsoil.
All plants large and small need ample space for root spread and your grass seed is no different than a towering tree or simple garden flower. By spreading your grass seed thickly on the ground, you encourage root competition as the seedlings grow. Some seeds push through quickly and take their share of the moisture and nutrients while others fail to grow a deep root structure at all. As a result, you have a patchy lawn that still struggles as the seedlings continue to fight for natural resources.
For those seedlings that do establish themselves in a highly competitive soil environment, their physical structure also suffers. Limited nutrients cause the grass stems and blades to have a thin shape. They cannot withstand foot traffic and harsh environmental conditions as they would with a uniform seed distribution. As a result, eventual summer temperatures will harm the grass and cause considerable dieback, even after several months of establishment.
Reduced Germination Rate
When you apply too much grass seed, each individual seed does not have the same access to the soil; some piled on top of other seeds may not touch the soil at all. Germination cannot successfully occur if the seed does not have soil contact. In fact, the excess seeds may also impede seedling growth of the seeds in full contact with the soil, which inhibits establishment and creates a slow-growing lawn. Normal grass seed germination typically ranges between one and three weeks, but stacked seeds on the soil make this time period significantly longer.
In general, you only need between 10 and 12 seeds within each soil square inch for grass varieties like fescue (Festuca spp.) and perennial ryegrass (Lolium perenne) which are easily grown in U.S. Department of Agriculture plant hardiness zones 4 through 8 and 3 through 9, respectively. With a good starter fertilizer and a moist soil structure, a proper seed application uses a broadcast spreader as you walk in one direction across your yard. After applying the seed in this direction, you turn to a 90-degree angle and spread the seed again. This strategy makes your seed distribution even and easily raked into the soil for proper contact. If you have a small area to seed, it is possible to spread the seeds by hand if you mix 4 parts sawdust to 1 part seeds, as the sawdust provides a medium to uniformly spread the seeds without bunching them into one area after hand dispersal.
University of Minnesota Extension: Lawn Renovation
University of Arizona Cooperative Extension: Spring Overseeding for High Elevation Cool Season Lawns
Lowe's: Seed Your Lawn
This Old House: When to Plant Grass Seed
Fine Gardening: Genus Festuca
North Dakota State University: Phytoremediation-Lolium Perenne