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Don’t Seed A Cool Season Lawn in the Summer

A scenario: Sometime between the end of May to the end of July you've noticed your lawn is in bad shape. You go to the garden center and see shelves full of grass seed. If the store is carrying seed that must mean it is okay to sow your new lawn at this time, so you purchase a bag or two. But what type of grass did you get? Cool season or warm season?

In my neck of the woods (Central Illinois) you will find cool season types of turf for sale. In fact, you will likely be hard-pressed to find any warm season grass seed in Central Illinois.

Cool season grasses are preferred in our area and northward because it tends to stay green for longer periods of the year. As the name implies, cool season grass grows actively in the spring and fall and will go dormant, turning a straw-colored brown, during the summer. Conversely, warm season type grass prefers the heat of summer and will only be green and actively growing during the hottest months of the year. (June, July & August)

Never mix warm with cool-season grass types. During any time of the year, you will wind up with patches of green grass and dormant grass.

The ideal time to sow warm-season grass is before the start of summer. Since this type of grass loves heat, this is the best time for establishment. The best time to seed a cool season lawn is the late summer to early fall.

A late season seeding of cool-season turf more conducive to its growth cycle because it gives the lawn the fall, winter, and spring to become established before facing the stressful heat of summer. A late summer to early fall sowing also beats out a spring seeded lawn due to:

  1. Warmer soil. In the spring, the ground is cold, and germination is not as efficient. Coming out of the summer, our soils are warm offering better germination.
  2. Less competition. Annual weeds are the biggest problem most homeowners face with a new lawn. By late in the season summer annual weeds will have completed their lifecycle and won't return until next spring when your late season planted lawn has more of a competitive edge.
  3. More food. Not food for your lawn. Food for the birds and rodents that eat lawn seed. At the end of the growing season, the landscape is flush with seed and other goodies for wildlife. Coming out of winter there is less food, so many birds and rodents (voles in my yard) will view your seed as a meal.

Let us assume you went ahead and seeded your lawn with a cool season mix in the middle of summer. Now, what do you do?

Once the seed germinates, it will likely be met with our delightful (blazing hot) Midwestern summer. High temperatures are not conducive for growth, and the seedlings may give out a few days past germination even with supplemental irrigation.

The only thing that can be done at this point is adequate irrigation. Supply an inch to two inches every week (depending on the weather conditions) to a lawn that is trying to establish. You could split these water application up over a few days of the week. My preference is to deliver an inch of water at one time and monitor the soil. When the top few inches dry out apply another inch. As a lawn establishes the best practice is to do infrequent, yet deep soakings.

Be prepared to do another round of seeding in the late summer to early fall. Dates that correspond best in Central Illinois are August 15 to September 15. Adjust by a week or two depending on your latitude for Illinois residents. Later in August for southern Illinois and earlier in August for northern Illinois.

Check out our University of Illinois Extension website LawnTalk for more information on lawn care, or contact your local Extension office.

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