- Whole Plant Traits: Plant Type: Ground Cover Herbaceous Perennial Ornamental Grass Leaf Characteristics: Semi-evergreen Habit/Form: Dense Erect Maintenance: Low Texture: Fine
- Cultural Conditions: Light: Full sun (6 or more hours of direct sunlight a day) Partial Shade (Direct sunlight only part of the day, 2-6 hours) Soil Drainage: Frequent Standing Water Occasionally Wet Available Space To Plant: Less than 12 inches Usda Plant Hardiness Zone: 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
- Fruit: Fruit Color: Red/Burgundy Fruit Type: Berry Fruit Description: After flowers bloom, red berries that are fleshy appear.
- Flowers: Flower Color: Gold/Yellow Green Insignificant Flower Inflorescence: Spike Flower Bloom Time: Spring Summer Flower Size: 3-6 inches Flower Description: These small, lateral flowers are green and yellow, blooming in mid-spring/ summer (around May to June) on a spadix that is about 3 inches long (2-4 inches).
- Leaves: Leaf Characteristics: Semi-evergreen Leaf Color: Green Leaf Feel: Glossy Leaf Value To Gardener: Fragrant Leaf Shape: Linear Hairs Present: No Leaf Length: > 6 inches Leaf Width: < 1 inch Leaf Description: In general, Acorus gramineus’s leaves are 1/4 inch wide, 6-12 inches long (but may be up to 18 inches long), narrow, linear, shiny/glossy, erect, smell sweet (fragrant), may be dark green, and speads by roots. This plant is grown for foliage. which smells sweet. Acorus gramineus ‘Oborozuki’ has long, arching downward, narrow, light green leaves (similar to grass).
- Stem: Stem Is Aromatic: No
- Landscape: Landscape Location: Container Naturalized Area Slope/Bank Small Space Woodland Landscape Theme: Rain Garden Rock Garden Water Garden Design Feature: Accent Border Foundation Planting Mass Planting Resistance To Challenges: Erosion Wet Soil
Japanese Sweet Flag Grass, Acorus gramineus: “Water’s Sedge”
Japanese sweet flag grass is one of those plants with a proclivity for water which also happen to resemble flowing water. This makes it much admired and appreciated, at least in my book. When I design around a water feature, whether it’s a tumbling waterfall, a bubbling urn or a meandering dry creek bed, I most always employ Acorus gramineus because this evergreen grass-like plant mimics the way water flows, cascades, and spreads out in a carefree way.
Japanese sweet flag grass, which belongs to the Acorus genus of wetlands grass, is a friendly species for a home garden. Its sibling common sweet flag (Acorus calamus) is a taller species which is useful at the edge of a pond or to stabilize marshy soil.
To learn whether your water feature or other garden areas should partner with Japanese sweet flag grass, please keep reading:
Above: Japanese sweet flag grass (Acorus gramineus) flows down a slope at San Francisco Botanical Garden. Photograph by Daderot via Wikimedia.
Native to Japan (where Acorus occurs in wetlands and shallow waters), this narrow-leaf, densely clumping perennial erupts from rhizomes that lie below the surface. The “sweet” part in the common name comes from the pleasant aroma the leaves emit when broken. Acorus is frequently used around the edges of water gardens and ponds; it is happiest when allowed to drink water without too many restrictions as it gracefully softens the look of rocks.
Above: When landscape architect William Dangar designed a garden for his own family (near Sydney, Australia), he incorporated a small backyard pond fringed by Japanese sweet flag grass. See more in Downsizing a House to Expand the Garden: At Home with Landscape Architect William Dangar. Photograph by Prue Ruscoe, courtesy of William Dangar.
Side note: I once planted A. gramineus ‘Ogon’ near a pond’s edge and watched the sedge slowly and quietly creep closer to the water. It decided to become one with the pond and to magically float and expand on the surface. Eventually, of course, I had to remove large sections of the grass-like plant after it overtook the pond and “naturalized,” but I admired its tenacity.
Above: Australia-based landscape architect William Dangar also uses Japanese sweet flag grass as a front-of-the-border ground cover. Here, in his own garden, it creates a gentle wave. Photograph by Prue Ruscoe, courtesy of William Dangar.
Indoors, Acorus can be kept as a houseplant, living in medium to direct light with high humidity and high water (the pot may even be allowed to stand in a shallow saucer of water). Because Japanese sweet flag grass is a marsh plant, water it plentifully to ensure the potting mixture is always thoroughly moist.
Above: On Washington’s Bainbridge Island, a path is edged with lime green Acorus gramineus ‘Ogon’ grass. In the foreground, yellow Sedum ‘Angelina’ and tall spires of Acanthus mollis create visual interest. See more of this garden in Water’s Edge: A Saltwater Courtyard Garden on Bainbridge Island. Photograph courtesy of Wittman Estes.
Best Acorus Varieties:
- Acorus gramineus ‘Ogon’ is a dwarf cultivar of A. gramineus which grows to 10 inches tall and spreads slowly. It has vibrant fans of glossy pale green and yellow-striped leaves to produce an overall lemony yellow effect.
- Acorus gramineus ‘Variegatus’ is a variegated-leaf form with attractive creamy white stripes on its green leaves. It looks lovely paired with silver-leaf plants and white blooming perennials. It grows to 10 inches tall and 6 inches wide, while slowly spreading.
- Acorus gramineus ‘Pusillus’ is a petite grass-like perennial, growing typically 2 to 3 inches tall, but perhaps a bit taller with rich soil and regular irrigation. Though spreading very slowly, it’s considered to have more of a clumping habit. Plant ‘Pusillus’ in full coastal sun to light shade and irrigate regularly or keep in shallow water. Also, because of its low stature it acts as an excellent plant between stepping stones in moist areas.
- Acorus gramineus ‘Pusillus Minimus Aureus’ features tufts of yellow grassy-like leaf blades and is a wonderful ground cover, forming a stunning golden carpet. Consider planting this between pavers in a partly shaded garden. Grows to 3 to 4 inches tall.
Above: ‘Ogon’ has a clumping form. A 6-inch plant in a 3-inch pot is $9.88 from 9EzTropical via Etsy.
- Japanese sweet flag grass is a beautiful accent plant or massed ground cover near water gardens, along streams or ponds, or in moist, open woodland gardens.
- The variegated varieties of Japanese sweet flag grass brighten partly shaded to fully shaded areas.
- Acorus be grown as a houseplant and as a companion in containers with other moisture-loving plants such as cannas, coral bells, and ferns.
- Deer leave this plant alone, thankfully.
Above: For wholesale purchases only, see Hoffman Nursery for Golden Variegated Sweet Flag.
Keep It Alive
- Plant Japanese sweet flag grass in full sun to full shade, but be aware that more sun equals higher water needs.
- Acorus grows well in both boggy conditions, including very shallow water and consistently moist garden soils. Scorched leaf tips will occur if the soil is allowed to dry out, subtly letting you know that you are depriving it.
- Trim blades to the ground if a Japanese sweet flag grass is looking tattered or unhappy.
- Propagate this perennial by separating overcrowded clumps in spring or summer. Carefully pull apart the clumps with your fingers, making sure that a medium-sized piece of rhizome is attached to each section and treat each divided clump as a plant.
For more growing tips, see Sweet Flag Grass: A Field Guide to Planting, Care & Design in our curated guides to Garden Design 101. Read more about how to use grasses in a landscape:
- Hardscaping 101: Ground Covers to Plant Between Pavers
- Grasses: A Field Guide to Planting, Care & Design
- Architect Visit: A Hazy Landscape of Grasses in Santa Monica
Sweet Flag Care: Tips For Growing Sweet Flag Grass
Japanese sweet flag (Acorus gramineus) is a striking little aquatic plant that tops out at about 12 inches. The plant may not be statuesque, but the golden-yellow grass provides plenty of bright color in soggy garden spots, along streams or pond edges, in semi-shady woodland gardens – or nearly any area where the plant’s moisture requirements are met. It is a good choice for stabilizing the soil in damp, erosion-prone soil. Read on for more information about Japanese sweet flag.
Arorus Sweet Flag Info
Japanese sweet flag, also known as Calamus, is native to Japan and China. It is a cooperative, slow-spreading plant that attains a width of 2 feet in about five years. Miniature greenish-yellow blooms appear on spikes in spring and early summer, followed by tiny red berries. The grassy leaves emit a sweet, rather spicy aroma when crushed or stepped on.
Sweet flag is hardy to USDA plant hardiness zones 6 through 9, although some Acorus sweet flag info indicates the plant is tough enough for zones 5 through 11.
Sweet Flag Care
It doesn’t take much effort when growing sweet flag grass. Sweet flag plants tolerate light shade or full sun, although the plant benefits from afternoon shade in hot climates. However, full sun is best if the soil is extremely boggy.
Average soil is fine, but be sure the soil is consistently moist, as sweet flag doesn’t tolerate bone dry soil and may scorch. Similarly, the leaf tips may turn brown in periods of extreme cold.
To grow sweet flag in a pond or other standing water, place the plant in a container and set it in water less than 4 inches deep.
Sweet flag plant benefits from division in spring every three or four years. Plant the small divisions in pots and let them mature before transplanting them into their permanent locations. Otherwise, growing sweet flag grass is nearly effortless.
Sweet flags look like small ornamental grasses, but they’re actually related to calla (Zantedeschia). Grown for highly attractive foliage. Use in damp borders, at pond edges, in shallow water, or average garden soil. Propagate by dividing clumps in spring or fall.
- Native to the Northern Hemisphere.
- Sword-shaped leaves resembling those of bearded iris are 1 inches wide, 45 feet long, growing in a clump about 2 feet wide.
- Foliage is fragrant when bruised, as are the thick rhizomes.
- Variegatus has very showy white-edged leaves.
- Dies to the ground in winter.
japanese sweet flag
- Native to Japan, China.
- A trouble-free plant that prefers moist, fertile soil, either boggy or well drained.
- Fans of narrow, 6- to 12 inches-long semievergreen leaves rise from the ends of slowly creeping rhizomes; the plant eventually forms a rounded clump.
- Excellent for massing, combining with coarser-leafed plants, or growing in containers.
- Ogon is especially showy, with arching golden yellow leaves to 10 inches long; it looks great beside dark green, burgundy, or purplish foliage.
- Variegatus has white-striped green leaves; leaves of ‘Licorice’ are 112 feet long, with fragrance and flavor of licorice.
- Dwarf Acorus g.
- pusillus, 35 inches high, and lime-green ‘Minimus Aureus’, 23 inches high, spread very slowly and are useful between stepping stones or tucked into niches in a rock garden.