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Cogongrass
A federal noxious weed and one of the world's worst invasive grasses - cogongrass forms dense mats that exclude everything else and burns dangerously hot. Never plant it; this entry is for identifying, reporting, and controlling it.
Safety notes Cogongrass is not a food and is not chemically poisonous, but it carries two real hazards. Its stiff leaf blades have tiny silica serrations that cut skin, so wear gloves and eye protection. More seriously, its dense cured foliage is highly flammable and burns hotter and faster than surrounding plants - a severe wildfire fuel that can kill trees a normal fire would spare. It is a federal noxious weed, illegal to plant or move; never move rhizomes or soil that may carry them.
Overview
Cogongrass (Imperata cylindrica) is a federal noxious weed and ranks among the worst invasive grasses on Earth. Across the warm Southeast - especially the Gulf Coast - it forms dense, spreading mats that exclude nearly all other plants, degrading pastures, forests, roadsides, and natural areas into worthless monoculture. Its aggressive network of sharp white rhizomes makes it extremely hard to kill, and it spreads both by wind-blown seed and by those rhizomes.
Worse, cogongrass is a severe fire hazard. Its dense, cured foliage burns hotter and faster than surrounding vegetation - hot enough to kill trees that would survive a normal fire - and the rhizomes simply resprout afterward, so fire spreads and rewards it rather than controlling it. Because it's a federal noxious weed, moving, selling, or planting it is illegal, and new infestations should be reported to authorities. This entry is here to help you recognize, report, and control cogongrass - and to warn against the ornamental 'Japanese bloodgrass' form, which can revert to the invasive green plant. Never plant it.
The one thing to knowCogongrass (Imperata cylindrica) is a federal noxious weed and ranks among the worst invasive grasses on Earth.
Quick facts
For identification. Not a growing guide.
- Height
- 48 inRange: 24–72 in
- Spread
- 120 inRange: 24–600 in
- Cold
- Takes hard frostdamaged below 0°F
- Heat
- Struggles above 110°F
- Life cycle
- Perennial, lives about 30 years
- Self-sows
- Yes. Never let it set seed.
- Habitat
- Full sun · Part sun · Part shade, well-drained soil
Through the year
A field guide through time
Explore the stages to recognize this plant throughout its life.
Stage 1 of 3 · The recurring year
Dense rhizome mats (identify & control)
year-round, every year
Know this stage
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Recognize it: off-center midrib, sharp mats, no clear clumps
Cogongrass forms dense, circular-to-spreading patches of yellow-green to tan leaves 1-4 feet tall. Key clues: each leaf blade has a distinctly OFF-CENTER (not central) whitish midrib, blade edges are minutely serrated and sharp, and the patch has no obvious individual clumps - it's a solid mat fed by sharp white rhizomes just under the soil. A circular, spreading, clumpless grass patch excluding all other plants is a red flag.
-
Report it and get expert control - do not just mow
As a federal noxious weed, new infestations should be reported to your state agriculture department or extension office. Effective control is a multi-year campaign of repeated tillage and/or systemic herbicide targeting the rhizomes; mowing or burning alone stimulates regrowth. Never move rhizomes, soil, or equipment from an infested area without cleaning - fragments start new patches.
Months are typical seasonal windows; climate, variety, and plant age can shift them.
Hazards
Excluding Monoculture Mats (ecological harm)Severity High DisordernowSeason: year-roundCircular, spreading, clumpless grass patches excluding other plants, with off-center leaf midribs and sharp blades, expanding outward each year.
Circular, spreading, clumpless grass patches excluding other plants, with off-center leaf midribs and sharp blades, expanding outward each year.
Multi-year rhizome-targeted control (repeated tillage and/or systemic herbicide), then restore native cover; mowing and burning alone reward it.
Never plant it; report new infestations; treat isolated outlier patches early before they coalesce.
The core hazard is ecological: cogongrass forms dense rhizome mats that exclude nearly all native grasses, wildflowers, and tree seedlings, degrading pastures, forests, roadsides, and natural areas into worthless monocultures with little wildlife value.
Extreme Fire HazardSeverity High DisorderSeason: Nov–MarDense tan thatch of cured foliage, especially near structures or woodland, and extreme fire behavior in infested areas.
Dense tan thatch of cured foliage, especially near structures or woodland, and extreme fire behavior in infested areas.
Do not rely on burning (it rewards the rhizomes and endangers people); control the rhizomes chemically/mechanically and reduce fuel through management.
Do not plant it; control infestations before they build fuel; treat cured stands near buildings as a wildfire hazard.
A severe safety and ecological hazard: cogongrass's dense, cured foliage burns much hotter and faster than surrounding vegetation, killing trees and native plants that would survive a normal fire and threatening property, while its rhizomes survive fire and resprout, so burning spreads and rewards it.
Wind Seed & Rhizome-Fragment SpreadSeverity High DisorderSeason: Mar–SepNew outlier patches downwind of infestations, and fresh patches where soil or equipment was moved from an infested area.
New outlier patches downwind of infestations, and fresh patches where soil or equipment was moved from an infested area.
Target rhizomes with sustained tillage and/or herbicide, prioritize outlier patches to stop long-distance spread, and persist for several seasons.
Prevent seed set where possible; never move infested soil, fill, or dirty equipment; clean machinery leaving infested ground.
Why it spreads so far and resists control: cogongrass releases clouds of wind-borne seed that found distant patches, while sharp rhizomes expand each stand and regrow from fragments carried on moved soil, fill, and equipment.
Grower tips
Notes from growers, tagged with the zone they grow in. A person reads every post before it appears.
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