Crabgrass in Warm-Season Lawns: Complete Guide

Crabgrass is an annual grassy weed that spreads low to the ground in a distinctive star or crab-like pattern, which is how it got its name. The stems radiate outward from a central point, and the plant can grow up to 2 feet in diameter if left unchecked. The leaves are wider and lighter green than most lawn grasses, with a distinctive horizontal growth habit that helps it avoid mower blades.

There are two main species in Florida: Large Crabgrass (Digitaria sanguinalis) and Smooth Crabgrass (Digitaria ischaemum). Both have similar growth habits but Large Crabgrass has more prominent hairs on its leaves and sheaths. The leaves are rolled in the bud (rather than folded like St. Augustine grass) and have a prominent midrib that's lighter in color than the rest of the leaf.

Crabgrass germinates from seed in spring when soil temperatures reach 55-60°F for several consecutive days - typically March in Florida. It grows aggressively through summer, producing seed heads from July through October. Each plant can produce over 150,000 seeds, which remain viable in the soil for years. The plant dies with the first frost in northern Florida but may persist year-round in South Florida's mild climate.

Crabgrass thrives in thin, weak lawns with compacted soil, poor drainage, or low fertility. It exploits any bare spots or thin areas in your turf, quickly filling in gaps where desirable grass is struggling. Hot, dry conditions that stress your lawn favor Crabgrass establishment because it's more drought-tolerant than most lawn grasses.