Annual Bluegrass

Annual Bluegrass

annual bluegrass
The photo is from Joseph M. DiTomaso, University of California - Davis, found at Bugwood.org.

Weed - Poa annua is known as Annual Bluegrass, annual meadow grass, pasture grass, annual spear grass, plains bluegrass.

Description: A cousin to Kentucky bluegrass, annual bluegrass has the same boat-shaped tip. It is a bunch grass, so that it does not spread by rhizomes like Kentucky Bluegrass. Annual bluegrass is folded in the bud, has a membranous ligule, with no auricles. The Blades are 1/8 inch wide and can grow to about 10 inches tall. The color is a light green. It can still produce seed if mowed as low as ¼ inch tall, and will produce flowers continuously. Sometimes the blades are crinkly on the lower part. Some of the stems are flattened at the base. This grass grows faster than Kentucky bluegrass and usually dies when it gets hot, creating unsightly brown spots in the turf and landscape. It is tolerant of extremes of pH, from acid to alkaline. Annual bluegrass does well in compacted soil as well as in well-drained fertile soil.

Flowers: an open panicle.

Similar plants: Rough Bluegrass (Poa trivialis), Kentucky Bluegrass (Poa pratensis), perennial annual bluegrass (Poa annua var. reptans).

Where: lawns, roadsides, gardens, moist areas, cultivated areas.

Propagation: Spreads by seed. It is considered a winter annual that germinates in the fall and overwinters as a small plant. It also will germinate in spring and throughout a cool summer. According to the Global Invasive Species Database website: Mature tall plants can produce 1,050 to 2,250 seeds per plant; mowed heights of ¼ inch can produce up to 360 seeds. Seeds can lie dormant for 6 years. Seeds can be spread by mowing, foot traffic, birds, and cultivation.

Poisoning: Not poisonous.

Historical: It is native to Eurasia and has become naturalized around the globe.

What: Seed can be produces a few days after pollination. It is considered to be one of the most widely distributed and reviled species in the world.

Cons: It can form mats that prevent desirable plants from germinating and growing. I could not find any herbal nor medicinal uses for annual bluegrass. One quote seems to say it all about its toughness making it hard to control: "Poa annua is supreme among weeds. It shows greater phenotypic and genotypic variability than most, if not all, other weeds; it flowers and fruits throughout the year; it germinates rapidly, and is small enough to escape notice. Its seeds are readily dispersed in mud sticking to shoes, feet, implements, or garden crops and its self fertility and rapid life-cycle ensure that a single plant is enough to build up a large population within a year or two." Tutin. Watsonia. 4:1-10. 1957.

Pros: While most golf superintendents consider this a terrible weed, others use it for putting greens such as the Oakmont Country Club in Pennsylvania. It bounces back quickly. This plant has medium palatability as cattle fodder. Birds eat the seeds.

Mary Anna Anderson
Mary Anna Anderson
Nebraska Extension Horticulturist

Mary Anna Anderson served from 1997-2013 as a horticulturist with Nebraska Extension in the Douglas/Sarpy County offices.