Crabgrass is a common annual grassy weed that starts from seed each spring when soil temperatures consistently reach about 55 to 60 degrees Fahrenheit. Identifying the plant early is important because pre-emergent herbicides must be applied before or immediately following germination for effective control. Once the seedling establishes itself, management becomes more challenging, often requiring post-emergent products or hand removal. Understanding the visual characteristics of the young plant is the most reliable way to prevent a widespread infestation.
Key Visual Cues of Young Crabgrass
The earliest sign of crabgrass is a small, light green seedling that can easily be mistaken for desirable turfgrass. The first true leaves that emerge are notably wider than most lawn grass blades, sometimes described as a small rectangle. These young leaves are fine-textured and often appear a lighter or yellowish-green hue compared to the established lawn. This helps them stand out in dense turf.
A defining characteristic for the most common species, large crabgrass (Digitaria sanguinalis), is the presence of fine hairs. These hairs are visible along the leaf blades and on the leaf sheath, which wraps around the stem. A membranous structure called the ligule is also large and prominent where the blade meets the sheath. This structure is a significant identification marker for grass weeds.
The growth habit of the young plant is a key identifier, as the leaves immediately begin to spread out low to the ground. This low-growing, sprawling pattern is what gives the weed its name, with shoots radiating outward from a central point. If you pull a young plant, you may notice a reddish-purple tint at the base of the stem near the soil line. This coloration is often observed in both large and smooth crabgrass species.
How to Distinguish It From Other Lawn Weeds
Distinguishing young crabgrass from other common grassy weeds requires focusing on distinct features. Goosegrass (Eleusine indica), which is also an annual weed, often appears a few weeks after crabgrass and has a noticeably different structure. Goosegrass stems are flattened and have a whitish base, unlike the rolled and often reddish base of crabgrass.
Another weed sometimes confused with crabgrass is perennial tall fescue, which also has wide, coarse blades and grows in clumps. Tall fescue is a perennial, meaning it is present year-round, while crabgrass is an annual that dies off in winter. Unlike the sprawling, low-to-the-ground growth of crabgrass, tall fescue blades typically grow straight up, creating a coarse, upright tuft. This tuft is present even before crabgrass has germinated.
Progression to Maturity
As summer progresses, the young crabgrass plant transitions into its mature form, changing its visual presentation. The initial fine leaves give way to longer, wider, and coarser blades that develop a darker green color. The plant’s sprawling nature intensifies, creating dense, matted clumps that can choke out desirable turfgrass.
The final stage involves the development of characteristic seed heads, typically appearing in late summer or early fall. These seed heads resemble small, thin spikes or “fingers” that extend outward, and a single mature plant is prolific, capable of producing up to 150,000 seeds.