The term “winter grass” refers to turfgrasses that maintain active growth when other varieties have stopped, allowing the lawn to remain green despite freezing temperatures. This green appearance during the dormant season often leads to confusion about whether the growth is a desirable grass, a weed, or a specific type of plant that thrives in winter.
The Category: Defining Cool-Season Grasses
The grasses commonly called “winter grass” are formally known as cool-season grasses, a classification based on their unique physiological needs. These plants grow most vigorously when air temperatures range between 60 and 75 degrees Fahrenheit, typically occurring in the spring and fall. Unlike warm-season counterparts, they do not enter dormancy during cold months, allowing them to stay green. Cool-season grasses are adapted to regions with cold winters and mild summers, dominating the northern United States. Their ability to tolerate freezing temperatures and their extended growing season make them the primary turf choice for maintaining year-round color, especially in the transition zone where both hot summers and cold winters occur.
Common Varieties of Active Winter Grass
Homeowners seeking a green lawn through the winter rely on specific varieties of cool-season grasses, each offering distinct characteristics. Kentucky Bluegrass is a popular choice for high-quality lawns, known for its deep, emerald-green color and medium-fine texture. It has an aggressive network of underground stems called rhizomes, which allow it to self-repair and form a dense, durable sod. It is slow to establish, often taking around 14 days for the seed to germinate.
Perennial Ryegrass is frequently used in seed mixtures because it germinates quickly, often within a week, providing fast ground cover. It has a shiny leaf blade and is often used for overseeding dormant warm-season lawns to provide temporary winter color. Tall Fescue is recognized for its deep root system, which provides superior tolerance to drought and heat compared to other cool-season types. It is a bunch-type grass, spreading by tillering rather than rhizomes, and is valued for its coarser texture and resilience in high-traffic areas.
Understanding Warm-Season Grass Dormancy
The brown appearance of many lawns in winter is due to the natural dormancy of warm-season grasses, which thrive in temperatures between 75 and 90 degrees Fahrenheit. When soil temperatures consistently drop below 55 to 60 degrees Fahrenheit, these grasses enter a protective resting state. Dormancy is a survival mechanism where the plant stops leaf production and transfers metabolic energy into its roots and lower stems. This involves the breakdown of chlorophyll, resulting in the characteristic tan or brown winter hue. Common examples like Bermuda grass and Zoysia grass turn brown throughout the southern United States and the transition zone. Dormancy allows the grass to conserve resources until warmer temperatures return, typically when soil temperatures rise above 60 degrees Fahrenheit in the spring.
Winter Weeds Often Mistaken for Grass
Patches of green in a winter lawn are often annual weeds that germinate in the fall and continue to grow during the winter months. These winter annual weeds take advantage of the dormant state of warm-season lawns, facing little competition for light and nutrients. They are often mistaken for turfgrass because they are the only green plants visible against a brown background.
Annual Bluegrass, or Poa annua, is one of the most common offenders, often confusing homeowners because it looks similar to Kentucky Bluegrass. A telltale sign of this weed is the presence of numerous small, white, fluffy seed heads, even when mowed short. Other prevalent winter weeds include Henbit and Chickweed, which form dense, low-growing mats of green. Henbit is identifiable by its square stems and scalloped leaves that appear to encircle the stem, while Common Chickweed has small, bright-green, pointed leaves and forms a mat with white, star-shaped flowers in the spring.