Purple nutsedge

Purple nutsedge (Cyperus rotundus) is a grass-like perennial sedge with the unmistakable triangular (three-sided) stem of sedges, which can be felt by rolling the stem between the fingers. Leaves are arranged in sets of three from the base, are shiny and V-shaped in cross section, and characteristically taper abruptly to a stiff, boat-shaped tip rather than gradually narrowing; the leaves are typically shorter than or about equal to the flowering stem. The seedhead is reddish-purple to purplish-brown, distinguishing it from the yellow to straw-colored seedhead of yellow nutsedge. Belowground it produces chains of small, bitter, interconnected tubers (nutlets) strung along rhizomes, which is the defining trait separating purple nutsedge from yellow nutsedge, whose tubers form singly at rhizome tips.

In turf, purple nutsedge grows faster than the surrounding grass and produces upright, glossy, light-green shoots that stand above the canopy within days of mowing, creating a ragged, uneven, persistently weedy appearance. Dense colonies crowd and shade desirable turf, and because the underground tuber network is so extensive, infested areas decline in density and uniformity while the sedge steadily expands and resists ordinary control.

Purple nutsedge is a warm-season perennial that reproduces primarily and aggressively from an extensive underground network of rhizomes, basal bulbs, and especially chains of dormant tubers, with seed playing a minor role. The interconnected tubers can each sprout new plants and remain viable in the soil for years, so a single plant rapidly builds a dense colony. Shoots emerge and grow vigorously in warm conditions of late spring and summer, and the linked-tuber system makes it one of the most difficult weeds in the world to eradicate.

It thrives in warm climates and is favored by moist, poorly drained, or overirrigated soils, though established tubers also tolerate drought. Purple nutsedge invades wet low spots, overwatered turf, and any open or thinning turf in warm weather, and because it spreads underground it readily colonizes outward from an established patch and reappears after cultivation that fragments and disperses its tubers.