American Mannagrass
Glyceria grandis
Last reviewed: August 2026
Glyceria grandis, or American mannagrass, is a tall wetland grass that blooms from June through August and grows well in marshes, wet meadows, and along streambanks with part sun to full sun.
Toxicity unknown
American Mannagrass (Glyceria grandis) is not listed by the ASPCA Animal Poison Control Center (opens in new tab) or the other sources we check, so we have no verdict for it either way. Absence from those lists is not a clearance. If your pet shows symptoms after eating any plant, call the ASPCA at (888) 426-4435.
Light
part sun
Water
high
Size
24"–60" H × 12"–24" W
Bloom
Jun, Jul, Aug
Native to
AZ, CA, CO, CT and 33 more states
Before you buy
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American mannagrass is a tall native wetland grass that forms upright clumps with narrow green leaves. It produces delicate seed heads in summer and thrives in consistently moist to wet soils.
Growing American Mannagrass
Grow American Mannagrass in part sun and high water. Mature plants reach 24 to 60 inches tall and spread 12 to 24 inches wide. Expect moderate maintenance to keep it looking intentional in a front yard.
In an HOA neighborhood
American Mannagrass takes more care to keep looking intentional in a front yard. Maintenance level: moderate. Consider it for backyard or mid-zone beds rather than the street edge.
Works well in: backyard only.
- Requires consistently wet conditions that may create drainage concerns
- Can appear wild and unkempt compared to typical landscape grasses
- May spread aggressively in suitable wet conditions
Wildlife value
The seeds provide food for waterfowl and songbirds, while the dense clumps offer nesting habitat for wetland birds.
Common questions
- When does American mannagrass bloom?
- American mannagrass typically flowers from June through August, producing open, drooping seed panicles above the foliage.
- What kind of site does American mannagrass need?
- This grass does best in consistently wet to saturated soil in part sun to full sun, such as pond edges, ditches, and marsh margins.
- How tall does American mannagrass grow?
- Mature plants generally reach 3 to 5 feet tall, with arching leaves and tall flowering stems in summer.
- Does American mannagrass spread on its own?
- Yes, it spreads by rhizomes and self seeding in wet soil, often forming dense colonies over time in favorable sites.
- Is American Mannagrass HOA-friendly?
- American Mannagrass takes more care to look intentional in a front yard. Consider it for backyard or mid-zone beds rather than the street edge.
These answers were drafted with an AI model from this plant's data. Verify care details with a local expert.
Native range data from the World Checklist of Vascular Plants (Kew). Pollinator and host plant associations compiled from GBIF, iNaturalist, and published ecological literature.
If something looks wrong
Common plant problems, and what to check first
These come up on almost any plant. Each guide lists the likely causes in the order they are worth ruling out, with one thing to check before you act on any of them, and links to the source it came from.
- It is dying right after planting
- Leaves turning yellow
- Wilting even though I watered it
- Brown crispy leaf tips
- Bugs on the plant
Ready to grow American Mannagrass? Add it to your garden in Pollinator Patch to track it and get season-by-season care guidance.
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