Acorus gramineus
Sources last read 14 September 2026.
Not yet rated How forgiving it is has not been judged here yet.
Also called Dwarf Sedge, grassleaf sweet flag, Grassy-Leaved Sweet Flag, Japanese Rush, Japanese Sweet Flag, Japanese Sweetflag and Slender Sweet Flag.
Toxicity is partly unassessed
- Not assessed for cats. This plant is not on the ASPCA list. That is not a finding of safety: none of the sources read for this site gives an answer either way. Treat it as unknown.
- Not assessed for dogs. This plant is not on the ASPCA list. That is not a finding of safety: none of the sources read for this site gives an answer either way. Treat it as unknown.
- Not assessed for people. RHS publishes no harm statement for this plant. That is not a finding of safety: none of the sources read for this site gives an answer either way. Treat it as unknown.
What the sources say about its care
Sources file this plant under other names: Acorus gramineus 'Variegatus' (v). Citations below point at the name its source uses.
- Light
- Full sunRHS · read 13 September 2026
- Water
- Poorly-drainedRHS · read 13 September 2026
- Humidity
No source read publishes a humidity figure for any plant on this site. What follows is general guidance for foliage plants.
ASHRAE recommends indoor relative humidity between 30% and 60% 30–60%Penn State Extension · read 13 September 2026- Temperature
How cold this tolerates, not what it prefers. No source read for this site publishes a preferred range for a plant indoors.
H6 — -20 to -15°C -20 to -15 °CRHS · read 13 September 2026- Soil
- Chalk, Clay, Loam; pH Acid or Alkaline or NeutralRHS · read 13 September 2026
- Toxic to cats
- Not on the ASPCA list. That is not a finding of safety.ASPCA · read 13 September 2026
- Toxic to dogs
- Not on the ASPCA list. That is not a finding of safety.ASPCA · read 13 September 2026
- Harmful to people
- No statement of harm to people is published for this plant; that absence is not evidence it is safe.RHS · read 13 September 2026
Routine care
- Watering
- Plant beside streams, ponds, bogs, water banks and in wet woodland. It works as an edging groundcover, and can be grown in a container provided the soil stays moist.NC State Extension · read 13 September 2026Can be grown in baskets set in shallow water to a depth of 10cm. It also works well in aquariums, but lives only a short time if the water stays above 22°C for extended periods.RHS · read 13 September 2026
- Propagation
- Divide in spring.RHS · read 13 September 2026
- Pruning
- If needed, tidy foliage that is old or damaged in early spring.RHS · read 13 September 2026
- Pests and diseases
- Usually free of pests and diseases.RHS · read 13 September 2026
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Photographs
About the plant
Acorus gramineus, commonly known as Japanese sweet flag, Japanese rush, grassy-leaved sweet flag, and grass-leaf sweet flag, is a botanical species belonging to the genus Acorus, native to Japan, Korea, and eastern Asia. The plant usually grows in wetlands and shallow water.
From Wikipedia, CC BY-SA 4.0 · read 13 September 2026
- Native range
- E. Himalaya to Japan and PhilippinesWorld Checklist of Vascular Plants, June 2026 release, CC BY.Kew WCVP · read 13 September 2026Japan, Korea and eastern AsiaNC State Extension · read 13 September 2026E Himalaya to Japan & PhilippinesRHS · read 13 September 2026
- Climate
- temperateWorld Checklist of Vascular Plants, June 2026 release, CC BY.Kew WCVP · read 13 September 2026
- Growth form
- perennial or rhizomatous geophyteWorld Checklist of Vascular Plants, June 2026 release, CC BY.Kew WCVP · read 13 September 2026Ground Cover, Herbaceous Perennial; habit arching, dense, erectNC State Extension · read 13 September 2026Clump forming (semi evergreen)RHS · read 13 September 2026
- Size
- Height 6–12 in; width 6–12 inNC State Extension · read 13 September 2026Height 0.1-0.5 metres; spread 0.1-0.5 metres after 2–5 yearsRHS · read 13 September 2026
- Flowering
- Flowers gold/yellow, green, insignificant; blooms in spring, summerNC State Extension · read 13 September 2026
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Sources
- ASPCA · read 13 September 2026
- Kew WCVP · read 13 September 2026
- NC State Extension · read 13 September 2026
- Penn State Extension · read 13 September 2026
- RHS · read 13 September 2026
- Wikipedia · read 13 September 2026
What this does not cover
The figures above are what published sources say, not measurements of the plant in your room. They say nothing about your pot size, your water, the season, or how far from the glass the plant stands, and those decide more than any figure here does.
Humidity has no species figure because no source read for this site publishes one, and the only temperature published for this plant is a cold floor. The simulator fills those gaps with general figures for its kind of plant, marked as general and listed on how we read sources. Where a toxicity row says the plant was not assessed, that is the absence of a finding and not a finding of safety.
If something is already wrong, the diagnosis tool asks about the soil, the window and the watering, which is where the answer usually is.