Wood bluegrass (Poa nemoralis)

Common Names: Eurasian woodland bluegrass

Description:

Wood bluegrass (Poa nemoralis) is a slender, tufted perennial grass from Europe and Asia, introduced to North America and now common in mixed woodlands of the northeastern United States [1][2]. Unlike many lawn and pasture grasses, it thrives in shade and grows well under a forest canopy, spreading slowly west from its northeastern foothold [1]. MISIN tracks it as a non-native to watch in woodlands and along forest edges.

Habit:

Wood bluegrass is a slender, upright bunchgrass, usually 1 to 2.5 feet tall, that grows in tufts without spreading by underground stems (rhizomes) [1]. Its leaf blades are narrow ? about as wide as a few sheets of paper stacked together ? and feel finely rough or sandpapery rather than hairy [1]. It flowers in an open, spreading seed head made up of many small, flattened spikelets [1]. It is easiest to notice in late spring through summer, when its open seed heads show above the narrow leaves in a shaded woodland understory, roadside, or forest edge [1].

At-a-glance cues:

1. Slender, upright bunchgrass, 1 to 2.5 feet tall, growing in tufts with no spreading rhizomes [1]
2. Narrow leaf blades, finely rough to the touch rather than hairy [1]
3. Open, spreading seed head with small, flattened spikelets, late spring through summer [1]
4. Grows well in shade ? a grass of woodland understories, not just open lawns [1]

Leaves:

1. Arrangement: alternate along the stem, typical of grasses [1]
2. Shape: narrow, flat blades [1]
3. Margin: rough-edged with tiny prickles rather than true hairs [1]
4. Surface: sandpapery-rough to the touch on both surfaces [1]
5. Size: blades about 1/3 to 1 inch (0.8 to 3 mm) wide and 2 to 4.5 inches (5 to 12 cm) long [1]
6. Ligule: very short, about 0.01 to 0.04 inch (0.2 to 1 mm), a thin membrane with fine hairs ? much shorter than in close relatives like fowl bluegrass [1]

Stems:

1. Habit: an upright, tufted (bunch-forming) perennial grass, 1 to 2.5 feet (30 to 80 cm) tall [1]
2. Growth form: grows in dense clumps with slender roots only ? no spreading rhizomes [1]
3. Cross-section: rounded, slender stems typical of grasses

Flowers:

1. Color: green to straw-colored, typical of grass flowers (no showy petals) [1]
2. Arrangement: an open, spreading seed head (panicle) 2.75 to 8 inches (70 to 200 mm) long and up to about 3 inches (18 to 80 mm) wide [1]
3. Spikelets: small, lance-shaped, 1/8 to 1/3 inch (3 to 8 mm) long, each holding 1 to 5 flowers [1]
4. Bloom time: late spring into summer
5. Each flower has both male and female parts [1]

Fruit and seeds:

1. Fruit type: a small, dry, one-seeded grain typical of grasses, enclosed in a bract (lemma) [1]
2. Lemma: awnless, with sparse, soft, tangled hairs at the base and a rough or finely hairy central ridge [1]
3. Ripening: summer
4. Dispersal: seeds are lightweight and scatter with wind, water, and on mowing equipment, clothing, and animal fur, as is typical for bunchgrasses

Habitat:

Wood bluegrass is native to Europe and Asia and was introduced to North America, where it is now naturalized and common in mixed woodlands of the northeastern United States, gradually spreading west [1][2]. It grows in riparian forests, moist to dry-moist upland forests, roadsides, and areas near homes and other disturbed ground [1]. Unlike sun-loving turf grasses, it tolerates shade well and is often found growing under a forest canopy [1].

Reproduction:

Wood bluegrass spreads by seed, and it often arrives the way many lawn and pasture grasses do: seed carried in soil, on mowing equipment, on shoes and clothing, or in grass seed mixes, since it is also sometimes sown in woodlands, parks, gardens, and playing fields for its ornamental value [1][3]. It grows in tight clumps and does not spread by underground stems, so a single plant stays put and grows outward slowly, while new plants establish from seed [1].

It flowers in late spring and summer and sets seed by mid-to-late summer. Because it does not spread aggressively by roots, catching and removing plants before they set seed is the most effective way to keep a patch from expanding.

Impact and Damage:

Wood bluegrass is not known to be a health hazard to people or pets, and because it is a slow, clump-forming grass rather than a spreading one, it is not a typical garden nuisance in the way running grasses can be. It is sometimes deliberately planted for its shade tolerance and fine texture in woodland lawns and parks [1].

In natural areas, wood bluegrass is a component of some forest understories in the northeastern US, where it grows under a wide range of native canopy trees [1]. No published, peer-reviewed study documents it aggressively displacing native understory plants in North America, so MISIN tracks it as a non-native to monitor and record rather than a confirmed major ecological threat.

Similar species:

Wood bluegrass belongs to a genus of grasses that are easily confused with one another; MISIN separately tracks several of its closest relatives.

Kentucky bluegrass (Poa pratensis) is the most widely grown bluegrass and the closest overall match, but it spreads by underground stems (rhizomes) to form a solid sod, unlike wood bluegrass's non-spreading tufts.

Canada bluegrass (Poa compressa) has flattened, blue-green stems, unlike wood bluegrass's rounded stems, and it also spreads by rhizomes.

Rough bluegrass (Poa trivialis) has rough-textured leaf sheaths and short, spreading runners (stolons) at the base, unlike wood bluegrass's smooth, non-spreading tufts.

Annual bluegrass (Poa annua) is a low, short-lived annual that flowers nearly year-round, unlike wood bluegrass's taller, longer-lived perennial growth with a single late-spring-to-summer bloom.

Monitoring and rapid response:

Signs to watch for:

1. Slender, upright grass tufts with narrow, rough-textured leaves growing in shaded woodland understories, forest edges, and roadsides, especially where nearby lawns or plantings could have been a seed source [1]
2. Open, spreading seed heads showing above the leaves from late spring through summer [1]

What you can do:

1. Hand-pull or dig small tufts, roots and all, while the soil is moist ? since the plant grows in clumps without spreading rhizomes, a full clump is usually removed in one go
2. Cut or mow before the seed heads ripen in summer to prevent new seed from spreading
3. Bag and remove cut seed heads rather than leaving them on site
4. Natural-area crews: remove scattered tufts in shaded understories before they seed, prioritizing areas near trails, roads, or plantings where new seed is most likely arriving

When to call a professional:

1. Large woodland areas with widespread establishment where hand removal is impractical
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Native Plant Trust Go Botany. Poa nemoralis (wood bluegrass). gobotany.nativeplanttrust.org
2. Plants of the World Online (Royal Botanic Gardens, Kew). Poa nemoralis L. powo.science.kew.org
3. USDA NRCS Plants Database. Poa nemoralis L. plants.usda.gov

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