A warm season grass is a classification of turfgrass adapted to thrive in high temperatures and intense sunlight. Native to tropical and subtropical regions, these grasses are primarily grown across the southern third of the United States, where the climate provides the long, hot growing season they require. They are defined by their ability to maintain growth and color during the hottest parts of the year, making them a popular choice for southern lawns.
Defining Characteristics and Seasonal Cycles
Warm season grasses utilize a highly efficient biological process known as C4 photosynthesis. This process allows the plants to more effectively convert sunlight and carbon dioxide into energy, especially under conditions of high heat and intense light. The C4 pathway minimizes water loss, making these grasses well-suited to hot, arid environments. Optimal growth occurs when temperatures are consistently between 80°F and 95°F, a significantly higher range than many other plant types prefer.
The seasonal cycle of a warm season grass is characterized by a pronounced period of dormancy during the cooler months. Growth begins in the late spring or early summer once soil temperatures rise consistently above 60°F. They experience their peak growth and deep green color throughout the summer before slowing down in the fall as temperatures drop.
These grasses enter dormancy, turning a tawny or light brown color, typically after the first frost or when ground temperatures fall below 65°F. This color change is a natural survival mechanism where the plant conserves energy until warm temperatures return the following spring. Dormancy is a protective state that allows the grass to withstand winter conditions.
How They Differ from Cool Season Varieties
The difference between warm and cool season grasses lies in their preferred temperature range for active growth. Cool season varieties grow best between 60°F and 75°F, thriving in the spring and fall, while warm season grasses require much higher temperatures. This distinction heavily influences the geographical areas where each type is most successful.
Warm season grasses dominate the Southern United States, while cool season grasses are prevalent in the North. The region between these two zones is called the “Transition Zone,” where both types can survive but face challenges, such as warm season grasses struggling with cold winters. Warm season grasses display superior drought and heat tolerance due to their C4 photosynthetic pathway, requiring less water compared to cool season grasses.
During winter, cool season grasses maintain a green color, even if growth has slowed considerably. Warm season grasses, however, enter dormancy and turn brown, which is the most visible difference between the two varieties. While warm season grasses require high water and nutrients during peak summer growth, their dormant period minimizes maintenance needs during colder months.
Identifying Popular Warm Season Grasses
Several common turfgrasses fall into the warm season category, each with distinct features. Bermuda grass is known for its aggressive growth and exceptional ability to withstand high foot traffic and intense heat. It is frequently used on sports fields and golf courses due to its resilience and ability to be mowed very short.
Another popular variety is Zoysia grass, which forms a dense, thick turf. It is notable for its good shade tolerance compared to Bermuda grass, and its dense growth habit helps resist weed invasion while requiring less water.
St. Augustine grass is easily identified by its broad, coarse leaf blades and thrives in the deep South. It is often preferred for its tolerance to salt and ability to grow well in shady areas.
Finally, Centipede grass is often marketed as a low-maintenance option and is most popular throughout the Southeast. This slow-growing grass has a light green color and requires less fertilizer than many other warm season varieties, making it a good choice for homeowners seeking minimal upkeep.