Cool-season grasses such as fescue or bluegrass do not enjoy high temperatures or prolonged periods of drought. These grasses are originally from cooler, more temperate regions of Europe.  Cool-season grasses make food using photosynthesis and nutrients from the soil but during very hot summers, they are much less efficient at the process and also use much more water than normal. We can help out our cool-season grasses during stressful conditions with a few good practices, however.

Watering our lawn in the summer is tricky. Deep, infrequent watering is always best. Depending on your soil type and how compact your soil is, it may mean that you leave a sprinkler on for several hours to get a good deep wetting. Deep watering promotes deeper roots, reduces growth rates, and conserves sugars. Just like people, grass has a hard time cooling itself in high temperatures and high humidity so be careful and resist the urge to water more frequently. 

Water in the morning if possible. The grass plant is very vulnerable to diseases when under the stress of high temperatures and drought. Wetting the leaf blade promotes fungal problems so we want the blade to dry as quickly as possible. Early watering allows the blade to dry very quickly. Watering in the late afternoon or evening also tends to hold heat in the soil longer, slowing down the soil cooling that typically happens after sunset.

Be very careful with any fertilizer application during the summer on cool-season grasses. Unlike zoysia or Bermuda, fescues and bluegrasses can easily be burned with nitrogen applications. Cool-season grasses slow down drastically during the summer and don’t need much food. Newer lawns often can benefit from a little nitrogen during the summer months but very little is needed.  Ideally, a slow-release nitrogen product will provide the best results in certain situations. 

Mowing during the summer should only continue as long as the grass is still growing. Drought and high temperatures will likely slow down growth and mowing should also stop. When we mow our lawns, it puts stress on the plant and in the spring, the grass is actively growing and recovers very quickly. When under stress such as high temperatures and drought, cool-season grasses likely will have a much harder time recovering. Keep your blades sharp and change up mowing directions to reduce damage to dry, hot lawns.

Very often our cool-season grasses will develop some disease problems during the summer. This is normal and the grass will typically recover when cooler weather prevails. Sometimes, however, disease treatment is necessary. Contact your local Extension Service for help identifying the disease present and proper control measures.

Overall, fescues are quite tolerant of Kentucky’s summers. Even with prolonged hot, dry periods, fescues recover nicely in the fall. Don’t be alarmed if your fescue turns brown and goes slightly dormant this summer. This is a natural occurrence even with cool-season grasses. 

Source: Andy Rideout, Henderson County Horticulture Agent