Lawns and other turf in Greater Columbus typically experience a summer slump sometime in late July or August, when the cool-season grasses, which make up most lawns, sharply reduce their growth rate, and their lush green color of spring fades to shades of yellow and gold.
This year, the lack of rainfall in the second half of June coupled with more than a week of temperatures in the high 90s, have caused most lawns in Greater Columbus to enter a summer slump several weeks early, just as the calendar signaled the beginning of meteorological summer.
While the lack of soil moisture was challenging for lawn grasses, it was the unrelenting heat for more than a week which sealed the dormancy deal for lawns in Greater Columbus.
On days when temperatures were in the high 90s, up to a quarter inch of soil moisture was lost every day to the increased rate of evapotranspiration which accompanies the increased temperatures. When precipitation or irrigation does not frequently and regularly replace this lost soil moisture, grass plants are forced to give up and go dormant in order to live and fight another day!
Brown grass is not dead
While the yellow and brown blades of grass may look dead, most healthy grass plants have entered dormancy in response to the hot and dry soil conditions. This is a natural drought resistance mechanism found in cool-season grasses.
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Most of these plants will break dormancy and begin to actively grow again when soil moisture levels get recharged. Ambient temperatures have moderated for now and if regular precipitation or irrigation provides moisture, most grass plants will recover.
We saw a little of this same pattern last year when June turned dry. Once regular rainfall returned in July, we saw a pretty quick green-up of most lawns. We did not experience extremely high ambient temperatures last June, so the dormancy was not as widespread or pronounced.
Grass plants, which were already unhealthy or under stress before conditions turned hot and dry late last month, may be slower to recover once soil moisture is replenished and some plants and even portions of entire lawns may not recover if they lack sufficient root reserves to begin and sustain active growth.
In these instances, renovation with spot seeding this fall is the best option for repair. It is just too challenging to successfully reseed during the warm, dry conditions of midsummer.
Irrigation can be challenging
Unless a homeowner started regularly irrigating the lawn before the hot, dry weather started forcing grass plants to shut down their vascular systems and enter dormancy, it can be a challenge at this point in time to begin irrigating the lawn and expect a quick response.
Because the soil is so dry, it can be extremely difficult to get water to infiltrate the soil, so you only want to apply as much irrigation water as can be infiltrated into the soil.
On a typical summer day, we can expect evapotranspiration to remove approximately one-quarter inch of moisture from the soil each day. On days when ambient temperatures reach the mid 90s, up to a quarter inch of soil moisture may be lost.
When this happens for seven or eight days in a row as it did a couple of weeks ago, you can see how soils can become completely devoid of moisture.
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If you do irrigate the lawn before regular rainfall returns, irrigate with greater frequency and a short duration in order to improve infiltration and reduce runoff.
Consider the use of a timer to start irrigating before sunrise so that irrigation is completed by early morning in order to reduce the amount of time that leaf blades are wet. Especially during periods of hot temperatures, extended periods of time that leaf blades remain wet will increase the growth of pathogens, which cause foliar diseases on turf grasses.
Enjoy the break from lawn maintenance
When grasses are under heat stress and go dormant, it makes little sense to continue to run the lawn mower over the lawn. Even if some plantains or other weeds which thrive in hot, dry conditions pop up giving the lawn an untidy appearance, we can actually do more harm than good by continuing to run equipment over grass plants.
In fact, even foot traffic can damage stressed grass plants, especially during the hottest part of the day. If you must address some untidy areas of the lawn right now, consider using a string trimmer to eliminate and weeds which pop up.
Applications of fertilizers and herbicides should also not be made during periods of hot weather and when plants are under drought stress. So, until the rain returns and cooler weather stimulates new growth, park the mower and lawn spreader, grab your favorite cool beverage and enjoy the time off from mowing and other lawn maintenance.
Mike Hogan is Extension Educator, Agriculture and Natural Resources and associate professor with Ohio State University Extension.
hogan.1@osu.edu
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