Annual Meadow-grass (Poa annua) — identification, habitat & look-alikes

Annual bluegrass, known in Britain as annual meadow-grass, is the small, bright green grass that shows up in lawns, sidewalk cracks, and golf greens. It can sprout, flower, and drop seed in about six weeks, which is why it is so hard to get rid of. In the US, gardeners and turf managers often just call it poa.

Appearance

Appearance: Unmowed plants usually reach about 4–10 in (10–25 cm). Stems are pale green, flattened, and bent at the base. Leaves are soft, 1–3 in (2.5–7.5 cm) long, often crinkled partway along, with a boat-shaped tip.
Growth form: Mostly a cool-season annual that sprouts in late summer or fall, once the soil cools below about 70°F (21°C), and keeps sprouting through winter.
Flowers: Open, branched 1–4 in (2.5–10 cm) long, sometimes tinged purple. In spring they can give an infested lawn a whitish sheen.
Flowering time: Seedheads can appear from early fall to early summer, with most in spring. It flowers even when mowed very short.

Look-alikes

Kentucky bluegrassPoa pratensis

Look at the , the thin membrane where the leaf meets the stem: Kentucky bluegrass has a short, squared-off ligule, while annual bluegrass has a pointed, silvery one. Kentucky bluegrass won't survive being mowed below 1 in (2.5 cm), but annual bluegrass will.

Why they get mixed upBoth have boat-shaped leaf tips, and annual bluegrass blends right into Kentucky bluegrass lawns.

Rough bluegrassPoa trivialis

Rough bluegrass also has a pointed ligule, but it is less silvery. It is a perennial turfgrass that does best in moist shade and struggles in heat and drought.

Why they get mixed upSame genus, same boat-shaped leaf tips, and both turn up in cool-season lawns.

Where it lives

Typical habitats: Lawns and golf courses
Gardens and flower beds
Sidewalk cracks and roadsides
Cool-season crop fields
Range: Thought to have originated in Europe, it now grows in temperate regions worldwide and is one of the most common weeds of lawns and other turf across the US. It has even spread to islands near Antarctica.
Preferred conditions: Prefers moist spots in sun or part shade and tolerates hard, compacted soil. In warmer areas it usually dies in summer, but where summers stay mild and the turf is watered regularly, it can stay green all year.

Life cycle

Reproduction: Seedheads can form about six weeks after a seed sprouts. Plants keep reseeding even when mowed below 1 in (2.5 cm), which most lawn grasses can't tolerate.

Name and classification

About the name: It arose roughly 50,000 years ago as a hybrid between two other grasses, Poa supina and Poa infirma. That mixed origin helps explain why it is so variable.
Varieties and forms: An upright annual type (var. annua) makes lots of seed and is more typical of lawns. A low, creeping perennial type (var. reptans) roots at the joints, makes fewer seedheads, and is common on golf greens. The two are hard to tell apart.