Crabgrass is an annual weed that can quickly become a nuisance in a manicured lawn. Identifying this common grassy invader early in the season is the most effective approach to control its spread before the plant matures and produces thousands of seeds. Understanding what the seedling looks like when it first emerges helps homeowners protect their lawn from this aggressive competitor.
When Crabgrass Germination Occurs
The emergence of crabgrass is not strictly tied to a calendar date but is instead triggered by specific environmental conditions. Germination begins when the soil temperature at a 2-inch depth consistently reaches 55°F to 60°F for several consecutive days. This temperature threshold signals the start of the weed’s growing cycle.
This environmental cue often aligns with certain natural events. The full bloom of the forsythia shrub, with its distinctive yellow flowers, is a common visual indicator that soil temperatures are approaching the necessary range for crabgrass to sprout. Since this weed is one of the first summer annual grasses to germinate, applying a pre-emergent treatment before the soil consistently hits this temperature is key to controlling its presence later in the summer.
Identifying the Seedling Stage
When crabgrass first emerges, it presents a distinct appearance that sets it apart from desirable turfgrasses. As a monocot, the initial growth is a single, relatively wide, light green blade. Following this, the first true leaves appear, which are noticeably broader than the blades of most cool-season lawn grasses.
The color of the young plant is typically a pale, vibrant, or yellowish-green, standing out against the darker green of established turf. A defining characteristic, even at this early stage, is its prostrate, or low-to-the-ground, growth habit. The stems and leaves begin to sprawl outward rather than growing strictly upright.
You can observe features like the ligule, a small membrane at the junction of the leaf blade and the sheath. Large crabgrass (Digitaria sanguinalis) has fine hairs visible on the leaves and leaf sheaths, while smooth crabgrass (Digitaria ischaemum) is mostly hairless. These cues confirm the identity of the seedling, which will eventually mature into a plant with stems that radiate outward.
Comparing Young Crabgrass to Other Grassy Weeds
Mistaken identity is common because other grassy weeds can look similar to young crabgrass. One frequent confusion is with clumping perennial grasses, such as tall fescue, which form thick, coarse patches in a lawn. Tall fescue seedlings tend to have a darker, blue-green color and a much more upright, bunch-type growth pattern.
Young crabgrass lacks the strong, central growing point characteristic of perennial turfgrasses. Unlike crabgrass, which spreads flat along the soil, nutsedge is a grass-like weed that grows straight upward and has a distinct triangular stem when rolled between the fingers. The soft, wide, and light green nature of a crabgrass seedling contrasts with the rougher texture of unwanted perennial grasses.
Correct identification ensures that the proper control methods are used, as products designed for crabgrass often have no effect on perennial weeds like fescue or nutsedge.