Crabgrass, a pervasive warm-season annual grass, is one of the most common and frustrating lawn weeds homeowners face. Belonging to the Digitaria genus, this plant is known for its aggressive, mat-forming growth habit that quickly takes advantage of weakened turf. Understanding where crabgrass originates, both globally and locally in a yard, is the first step toward managing its persistent presence.
Global Origin and Classification
The most common crabgrass species infesting North American lawns are not native to the continent but are immigrants from the Old World. These two primary culprits are Large Crabgrass (Digitaria sanguinalis) and Smooth Crabgrass (Digitaria ischaemum). Both species originated in Eurasia or Africa and were subsequently spread around the globe.
Large Crabgrass, sometimes called hairy crabgrass, and Smooth Crabgrass are both summer annuals. The introduction of these species to the United States was often accidental, though Digitaria sanguinalis was even intentionally introduced in 1849 as a potential forage crop. Their ability to thrive in a wide variety of disturbed habitats, including lawns, golf courses, and gardens, allowed them to become globally established.
How It Arrives in Your Yard
The appearance of crabgrass in a specific yard is entirely dependent on the dispersal of its seeds. Seeds can be carried by numerous vectors from nearby infested areas.
One common way seeds arrive is by adhering to the tires of vehicles, the soles of shoes and boots, or the blades and decks of lawn maintenance equipment. Seeds can also contaminate soil, mulch, or topdressing materials brought into a yard for landscaping projects. Natural elements like wind or water runoff can carry the lightweight seeds across property lines from a neighbor’s lawn or nearby fields.
Once the seeds are deposited in the soil, germination is triggered by specific environmental cues. The primary trigger is soil temperature, which must reach 55°F for four or five consecutive days. The seeds will continue to germinate throughout the summer, though peak emergence occurs in the early spring.
The Key to Its Persistence
Crabgrass’s success lies in its prolific seed production and its adaptability to harsh conditions. A single, healthy crabgrass plant is capable of producing an estimated 150,000 seeds during its relatively short lifespan. This high output ensures a reservoir of dormant seeds, known as a seed bank, remains in the soil for future growing seasons.
Although the mature plants are killed off by the first hard frost of autumn, the seeds can remain viable in the soil for up to three years, waiting for the correct temperature signal to sprout. Furthermore, crabgrass is a warm-season (C4) plant, which allows it to tolerate the high temperatures and drought conditions of summer better than many cool-season turfgrasses. Its low-growing, tillering habit makes it highly resistant to typical mowing heights, allowing it to produce seeds even when the lawn is regularly cut.