Ryegrass, a common turfgrass species (Lolium), is used for both temporary and permanent lawns. Whether it survives the summer depends entirely on its specific species and local climate conditions. The two main types, Annual Ryegrass and Perennial Ryegrass, have fundamentally different life cycles and tolerances for summer temperatures. Understanding this distinction is crucial, as one type is intended to die out in the heat, while the other struggles to survive it.
Annual vs. Perennial Ryegrass: The Difference in Summer Survival
The fate of a ryegrass lawn in summer is determined by its classification as either annual or perennial. Annual Ryegrass (Lolium multiflorum), often used for temporary winter color, completes its life cycle within a single growing season. It is primarily sown in warm-season regions, such as the Southern United States, to provide green cover during the winter dormancy of grasses like Bermuda or Zoysia. As soil and air temperatures consistently rise in late spring and early summer, the annual species naturally dies out, which is the intended outcome.
Perennial Ryegrass (Lolium perenne) is a cool-season grass whose summer survival is uncertain. It is intended as permanent turf in northern climates where summers are mild, but it struggles in the heat and humidity of transition and warm-season zones. Growth slows drastically when air temperatures exceed 80°F, and severe stress occurs when soil temperatures rise above 85°F. In hotter regions, the perennial type often fails to survive the entire summer or enters a heat-induced dormancy that frequently leads to death.
The Physiological Impact of Summer Stress
Perennial ryegrass often succumbs to summer conditions due to its biological response to heat. Its optimal growth temperature range is 59–75°F (15–24°C); temperatures above this induce thermal stress. When air temperatures exceed 85°F, photosynthetic efficiency declines rapidly. Simultaneously, high temperatures promote respiration, causing the plant to consume stored energy faster than it can produce it. This leads to a net loss of carbohydrates, while high soil temperatures impair root function and inhibit water absorption.
Prolonged high temperatures, especially warm nighttime temperatures, prevent the grass from recovering energy reserves lost during the day. This sustained energy deficit, combined with reduced water uptake, weakens the plant and makes it highly susceptible to disease and insect damage. The result is often a complete collapse because the grass cannot sustain life through the summer months.
Strategies for Summer Ryegrass Management
Homeowners aiming to preserve Perennial Ryegrass through the summer must adopt specific, stress-reducing management practices.
Watering
Watering should be deep and infrequent, aiming to wet the root zone to a depth of four to six inches rather than shallowly wetting the surface. Watering early in the morning is the most effective strategy, as it minimizes water loss to evaporation and allows the leaf blades to dry before nightfall, which reduces the risk of fungal diseases.
Mowing Height
Raising the mowing height considerably, preferably to three inches or higher, is crucial. Taller grass blades shade the soil surface, helping to keep the soil and the plant crown cooler, which mitigates thermal stress. Taller grass also encourages a deeper, more robust root system, improving the plant’s access to soil moisture during dry periods.
Fertilization
Fertilization practices must be adjusted to avoid stimulating unsustainable growth during peak heat. Homeowners should reduce or eliminate nitrogen application during the summer, as high nitrogen promotes lush, tender growth that the heat and drought will quickly damage. Instead, focus on micronutrients and slow-release fertilizers in the late summer or early fall to prepare the turf for the following year.
In warm-season zones, the management goal shifts to transitioning from Annual Ryegrass to the underlying warm-season grass, such as Bermuda. This transition is encouraged by gradually lowering the mowing height and reducing water frequency as spring temperatures rise. Stressing the ryegrass causes it to die back, allowing the warm-season grass to emerge from dormancy and take over the lawn.