Tall fescue (TF) is a cool-season grass that thrives during the moderate temperatures of spring and fall. Its natural growth cycle slows significantly as summer temperatures rise, often leading to heat-induced stress and dormancy. When the grass enters this protective state, the blades turn brown, which is a common concern for homeowners. Maintaining a vibrant tall fescue lawn through the summer requires shifting maintenance practices, focusing on relieving heat stress rather than promoting aggressive growth. The primary strategies involve specific watering techniques, adjusting mowing habits, and carefully managing nutrients and disease risks.
Strategic Summer Watering
Watering technique is the most important factor in keeping tall fescue green during the summer heat. Shallow, frequent watering encourages a weak root system that is highly vulnerable to drying out. The goal is to utilize the deep-rooted nature of tall fescue, which requires deep and infrequent applications of water.
Apply enough water to saturate the soil to a depth of four to six inches, which usually equates to about one to one and a half inches of water total per week. This volume encourages the roots to grow downward, making the plant more resilient to surface heat and drought conditions. Rather than watering on a fixed schedule, monitor the grass for signs of stress, such as a dark bluish-gray color or wilted blades.
It is best to apply water early in the morning, between 4 a.m. and 10 a.m. Watering during this time allows the moisture to soak into the root zone while minimizing the time the grass blades remain wet. Watering in the late afternoon or evening can leave moisture on the leaf surface overnight, which creates an ideal environment for common turf diseases to develop.
Adjusting Mowing and Cutting Height
Physical maintenance, particularly the height of the cut, acts as a natural defense system for tall fescue against summer stress. Raising the mowing height to its maximum setting, typically between 3.5 and 4 inches, is essential during the warmer months. This longer blade length provides beneficial insulation and shade for the delicate crown of the plant and the soil beneath.
The taller grass helps to keep the soil cooler, conserving moisture by reducing evaporation from the surface. A taller blade also maintains the maximum leaf surface area for photosynthesis, which is crucial for energy production when the grass is under stress. Always adhere to the “one-third rule,” which dictates that you should never remove more than one-third of the total blade height in a single mowing session.
This rule prevents the grass from going into physiological shock, which can result in browning of the tips and reduced root growth. If the grass has grown too tall, it may require multiple mowing passes over several days to bring it down to the desired height safely. Using a sharp mower blade is necessary because a dull blade tears the grass, creating ragged edges that lose water quickly and invite disease.
Managing Summer Nutrient and Disease Stress
Summer is a period for survival, not vigorous growth, so nutrient management must be approached with caution. Avoid applying high rates of nitrogen fertilizer during the peak heat of summer, which generally spans July and August. Nitrogen stimulates top growth, forcing the plant to expend energy it needs to conserve for heat tolerance and root maintenance.
If any summer fertilization is deemed necessary, use a very low-nitrogen, slow-release formula. Alternatively, focus on micronutrients like potassium, which can help strengthen the plant’s cell walls and improve its overall stress tolerance. Excessive nitrogen can also increase the susceptibility of tall fescue to Brown Patch, the most common and damaging summer turf disease.
Brown Patch disease, caused by the fungus Rhizoctonia, thrives in conditions of high heat and high humidity, particularly when nighttime temperatures consistently exceed 68°F. The disease appears as circular or irregularly shaped patches of blighted turf. Prevention involves minimizing leaf wetness duration, which is why early morning watering is recommended.
In areas with historically high disease pressure and humidity, a preventative fungicide application may be necessary to protect the lawn. Ensuring good air circulation and soil drainage also limits the moist conditions that allow the Brown Patch fungus to flourish. Selecting tall fescue cultivars with high disease resistance is another proactive measure that reduces the need for chemical intervention.