When summer conditions become hot and dry, Kentucky bluegrass and other cool-season grasses turn brown and go dormant.
Dormancy is a natural survival mechanism for Kentucky bluegrass and other cool-season grasses. During extended dry periods, turfgrass foliage will cease growth and turn brown. While the foliage is dead, the turfgrass crowns and roots remain alive.
How Long Can Dormancy Last?
Generally, Kentucky bluegrass and other cool-season grasses can remain dormant for 4 to 6 weeks without suffering significant damage. Once weather cools and more moisture becomes available in the fall, the lawn will green back up and start growing more vigorously.
What if Hot Weather Persists Longer than Six Weeks?
Dormant lawns are in jeopardy of dying if dry conditions persist over an extended period. It's best to water the lawn if the turfgrass has been dormant for 4 to 6 weeks. Apply 1 to 1 1/2 inches of water in a single application. This will not cause the grass to green up, but it will keep the turfgrass crowns and roots alive.
If the dry weather persists, water the dormant lawn in the same way approximately every 4 weeks.
How Do I Keep the Lawn from Going Dormant?
Regular irrigation during the summer can keep lawns from going dormant. By providing approximately 1 inch of water a week, you can keep the lawn green. This regular irrigation requires frequent watering, and sometimes lawn watering bans would prevent this regular watering. In these cases, the lawn will go dormant.
Should the lawn go dormant and you want it to green up again, apply 1 to 1½ inches of water in a single application. Water again 7 days later. The grass should begin to green up after the second application. Continue to provide regular irrigation to keep the lawn green.
It is not advisable to allow the lawn to go in and out of dormancy through the summer months. Should the lawn go dormant, only bring it out of dormancy when you are able to maintain regular irrigation to prevent it from going dormant again.
How Do I Care for a Dormant Lawn?
Watering
To improve the survival odds for dormant lawns, apply (if possible) one-quarter-inch of water per week. This will not green up the lawn but should keep the turfgrass crowns hydrated (alive) until regular rains return.
Mowing
When lawns are dormant, very little growth occurs, reducing the mowing frequency. In summer, raise the mower blade to a height of 3 to 3½ inches.
If possible, avoid moderate to heavy foot or vehicular traffic on dormant lawns. Moderate to heavy traffic will likely damage the turfgrass crowns. Damaged plants may not fully recover when rain returns.
Fertilizing
It is generally not advisable to fertilize Kentucky bluegrass and other cool-season grasses during the summer months. Fertilizing a dormant lawn will not harm it, but the turfgrass may not receive the full benefit of the fertilizer application. In Iowa, spring, mid-September, and late October/early November are the best times to fertilize lawns.
The application of standard lawn care treatments to dormant lawns by lawn care professionals will not harm the turfgrass. In fact, the turf will likely benefit from the treatments when it emerges from dormancy.
Herbicides
Broadleaf herbicides are most effective when applied to weeds that are actively growing. Because of the dry conditions, most broadleaf weeds are also exhibiting stress symptoms (curled or wilted leaves). Applications of granular or liquid broadleaf herbicides are likely to be ineffective as most broadleaf weeds are not actively growing. In Iowa, mid-September to early November is the best time to apply a broadleaf herbicide to lawns.
How Do I Care for Newly Seeded or Sodded Lawns in Hot Dry Conditions?
It's advisable not to allow lawns established in the current or previous year (either by seed or sod) to go dormant. The root systems of recently established lawns are not as extensive as older lawns. Newer lawns may not survive dormancy.
If possible, water recently established lawns on a weekly basis. Apply 1 inch of water per week in a single application or one-half inch every 3 to 4 days.
What Do I Do if the Lawn Dies Due to Dry Conditions?
Any areas killed by dry conditions need to be reseeded. The ideal time to reseed is late August to mid-September.
Using a rake, remove some of the dead, dry grass so the soil is visible. Obtain seed that is a similar mix of species to what is already growing in your lawn.
Find a handful or two of soil from a garden area or from bagged topsoil and mix it with a couple of handfuls of grass seed. Mixing a small amount of garden soil with the seed helps ensure good seed-to-soil contact. Sprinkle this seed/soil mixture over the spot.
Water regularly until it germinates. Daily watering may be necessary if Mother Nature doesn't provide rain. The area should green up in two to four weeks; over time, the color and texture will fully blend with the surrounding grass.
More information can be found in this article: Overseeding a Lawn.
More Information
- Summer Lawn Care
- Late Summer and Fall Lawn Care
- Complete Guide to Watering Lawns
- Turfgrass Management Calendar: Kentucky Bluegrass Lawns (PDF)
- Lawn and Turfgrass Resources for Iowa
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