Late August to early September is the best time to overseed cool season grasses. It may still be a little warm, but temperatures will quickly begin to moderate as the days get shorter.
The easiest way to get new seed into your lawn is to core aerate it first before sowing seed across your lawn. Be sure to either wait until a decent rain has fallen or the lawn is watered well before aerating.
The goal is to allow the core tines to penetrate the soil to pull up plugs of soil and leave them back on top of the ground. This opens up the lawn for more air, water and nutrients to penetrate into the root zone to help build stronger roots.
It also provides a great place for seed to come in contact with soil in order survive after germination. Throwing grass seed across a lawn without proper preparation will provide poor or no germination.
You can hire someone to do the work for you or you can rent care aeration machines at rental centers, hardware stores and home improvement stores. The core aerator will not fit into the trunk of a car, so you either need access to a pick-up truck or a small tow-behind trailer. Use it just like a lawn mower, but be sure to mark sprinkler heads, buried cables and electric dog fences.
New seedlings germinate and grow best when soil temperatures are between 70 and 80 degrees. Purchase good quality seed and not a bag of cheap seed you find at a discount store. A good mix of seed will cost around $4 to $8 a pound. You may have to go to a landscape supply store or to a feed store to find quality seed. Many times the seed is available in bulk and you can purchase larger quantities.
Most seeding failures comes as the result of putting too much seed in too small of an area and not keeping the area moist for a long enough period of time. Perennial ryegrass will germinate in 5 to 7 days, turf-type tall fescue and fine-leafed fescues will germinate in 7 to 14 days and bluegrass takes 28 days. Once the grass germinates, it will need continual water to develop roots and shoots. Provide ½ inch of water to your lawn each week – more if it remains hot and dry.
Depending on the mix of seed you plan to use, the amounts sown per 1,000 square feet range from 3 to 6 pounds. Bluegrass is the smallest of seed, so it contains more seeds per pound. Ryegrass is the next largest followed by the fine-leafed fescues and turf-type tall fescue. The larger the seed, the more you will need to spread per 1,000 square feet.
After your lawn has been core aerated and overseeded, apply a fertilizer with an analysis of 16-4-8 or similar. In states that require phosphorus-free fertilizers, most allow fertilizers with phosphorus (the middle number on the analysis statement) to be used on newly seeded turf.
Check with your country extension service to see if your state allows the use of these fertilizers. You will want to apply a pound of nitrogen per 1,000 square feet. To determine the amount of fertilizer needed to apply per 1,000 square feet, divide 100 by the first number on the fertilizer bag. For example, if you purchase a 16-4-8 fertilizer, 100 divided by 16 equals 6.25. This means you will apply 6.25 pounds of fertilizer to provide 1 pound of nitrogen per 1,000 square feet.
Continue mowing as the new seed germinates. You want to make sure the sun reaches the new seed to help it germinate. As far as spraying for weeds, you need to wait until the new grass has been mowed two to three times before spraying for any weeds. If you are very careful, you could spot spray a few broadleaf weeds, such as a dandelion, but do not spray across the entire lawn.
You may find it easier to contact your neighborhood lawn care professional at Spring-Green to do all this work for you, except for the mowing. Don’t wait as there is a limited amount of time to get this work completed until it gets too cold for good germination.