Acorus gramineusJapanese Sweet Flag

Acorus gramineus, the Japanese Sweet Flag, is a low, evergreen, grass-like perennial that spreads slowly by a creeping rhizome to form a dense mat of narrow, fan-arranged leaves. The foliage carries a sweet spicy scent when bruised, and the plant holds its colour through the year wherever the ground stays damp. It is not a true grass, but it is used exactly as one in planting schemes.

Specifiers reach for it at the wet edge of a scheme, where turf fails and a marginal aquatic is too coarse: pond and stream margins, rain gardens, swale bases and the shaded damp ground under trees.

Specifications

• Height0.2 to 0.4 metres
• Width0.3 to 0.5 metres, spreading slowly by rhizome
• Native toEast Asia, including Japan, Korea and China
• FoliageNarrow, arching, strap-shaped leaves held in flattened fans, mid-green and aromatic when crushed; evergreen
• Growth rateSlow to moderate

Conditions

• SoilPrefers consistently moist to wet, humus-rich soils; tolerates shallow standing water and heavy ground
• LightFull sun to partial shade
• WaterHigh; needs permanently moist soil and is not drought-tolerant
• ClimateThrives in temperate and subtropical regions; frost hardy

Additional Features

• FormDense, low, fan-leaved clump that knits into a continuous mat
• UsesIdeal for pond and stream margins, rain gardens, swale planting, damp shaded ground cover and soft edging to water features
• SpacingPlant 0.2 to 0.3 metres apart for a closed mat within two seasons
• Low MaintenanceCut back tired foliage in late winter; divide congested clumps every few years
• Pest ResistanceGenerally trouble free
• VersatilityWorks as a marginal aquatic in shallow water or as a ground cover in permanently moist borders

Japanese Sweet Flag is the reliable answer to the damp, part-shaded ground that defeats most ground covers.