Rough bluegrass

What is rough bluegrass?

Rough bluegrass (Poa trivialis), also called roughstalk bluegrass, is a cool-season perennial from Eurasia. It is in the same genus as Kentucky bluegrass and looks a lot like it, but it spreads by stolons above the ground instead of rhizomes below it.

Its strength is shade on wet soil, where few lawn grasses do well. Rough bluegrass grass does poorly in heat, drought and foot traffic, so in sunny lawns it tends to thin out in summer and leave light, patchy areas.

Penn State says its light color and habit of forming patches mean it is generally kept out of seed mixtures. NC State notes it can become an aggressive spreader in full sun and is often called a weed in lawns and on golf courses.

How to identify rough bluegrass

Pull up a few shoots and look closely where the leaf blade meets the stem. Here is what to check on rough bluegrass:

• Vernation: Folded in the bud.
• Ligule: Thin membrane, long and sharp-pointed, 4 to 6 mm (0.16 to 0.24 in.), may have hairs on the edge. Kentucky bluegrass has a short, even ligule.
• Auricles: None.
• Collar: Distinct and split by the midrib.
• Leaf tip: Boat-shaped and sharply creased.
• Leaf blade: 1 to 4 mm wide, glossy underneath, rough edges at least near the tip, with a clear line on each side of the midrib.
• Sheath: Open only part of the way.
• Seedhead: Panicle with flat spikelets holding 2 to 3 seeds each.
• Growth habit: Spreads by above-ground stolons; no rhizomes.

Where rough bluegrass is grown in the US

Rough bluegrass has one real lawn job: wet shade. Penn State suggests it only for heavily shaded lawns with poorly drained or moist soil, seeded alone at 2 to 3 lb per 1,000 sq ft. UMass uses a wet-shade mix of about 70 percent rough bluegrass and 30 percent shade-tolerant Kentucky bluegrass.

It also has winter overseeding uses. NC State says it is sometimes sown alone or with perennial ryegrass to overseed bermudagrass putting greens, since it handles mowing below 3/16 in. UC IPM says it can overseed dormant bermudagrass and is used for shaded turf in California's fog belt. The University of Minnesota lists it, with supina bluegrass, as an option for dense, moist shade, but notes the seed is expensive.

Most of the time, though, it shows up as a weed. NC State's plant toolbox says it is often treated as a weed in lawns and on golf courses and is listed as invasive in Virginia, Pennsylvania and Alaska. In sunny lawns it can spread and crowd out other grasses, then turn into light, patchy areas in summer. See our weed identification guide for other lawn weeds.

Rough bluegrass pros and cons

Pros

• One of the few lawn grasses for wet, heavily shaded spots
• Spreads by stolons to fill in
• Handles very low mowing on golf greens

Cons

• Light color and patchy look; generally kept out of mixes
• Poor heat, drought and traffic tolerance
• Often becomes a weed in sunny lawns
• Listed as invasive in Pennsylvania (NC State Extension)
• Prone to brown patch, rust, stripe smut and snow molds
• UC IPM says it is susceptible to most turfgrass insects and diseases

Grasses that look like rough bluegrass

How and when to plant rough bluegrass

Ways to plant: Seed (Penn State, UC IPM).

Seeding rate: 2 to 3 lb per 1,000 sq ft (Penn State; also the UMass wet-shade mix rate). UC IPM gives 1 to 3 lb.

Seeding dates change from state to state. See when to plant grass seed by state, or our Pennsylvania grass seed guide if you are in PA.

How to care for rough bluegrass

Mowing: Mow at 1.5 to 2.5 in. (Penn State).

Watering: It needs rich, moist soil and a lot of water (UMass, UC IPM). UC IPM advises frequent watering; it has shallow roots and does poorly in drought.

Fertilizing: Plan on about 2 to 3 lb of nitrogen per 1,000 sq ft per growing season (Penn State).

Nitrogen per year: 2 to 3 lb N per 1,000 sq ft per growing season (Penn State); UMass and UC IPM list about 2 to 4 lb.

Overseeding: Use it only for heavy shade on poorly drained soil (Penn State), alone at 2 to 3 lb per 1,000 sq ft or in a wet-shade mix with shade-tolerant Kentucky bluegrass (UMass). If it is an unwanted weed, NC State's cultural steps are to keep the desired turf thick, use clean seed, and dig out or sod-cut patches. A non-selective weed killer would also kill the grass around it; use only products labeled for this use, and the label is the law. For chemical control, hire a licensed pesticide applicator.

Common rough bluegrass problems

If a pesticide is needed, use only products labeled for that use; the label is the law. If you hire someone to treat a lawn, make sure they hold your state’s pesticide applicator license; see our pesticide applicator license guide. To put a name to a lawn weed, use our weed identification guide.

Questions we get about rough bluegrass

Similar lawn grasses

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