How to Grow Acorus – Sweet Flag

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Acorus, commonly called sweet flag–is a wetland perennial that is both grass-like and iris-like. It produces clumps of strap-shaped leaves and bears small nearly insignificant flowers that jut from leaf-like flower stalks.

Acorus grow from rhizomes. It grows best in wet soil or standing water. It is a colorful choice to grow the margins of ponds or bogs. Acorus spread steadily but is not invasive.

Acorus gets its common name “sweet flag” from its flag-like, iris-leaf-like leaves. It is more closely related to jack-in-the-pulpits (Asarum) than to flags or irises.

Acorus rhizomes can be dried and ground for use as a fixative in potpourri. The leaves, which have a slightly sweet, spicy fragrance, have been used as a strewing herb. 

Acorus is a genus of 2 species of rhizomatous marginal aquatic perennials. They are native to shallow water and stream throughout the Northern Hemisphere, particularly East Asia.

Get to know Acorus

  • Plant type: Perennial
  • Growing zones and range: Zones 4 to 11
  • Hardiness: Hardy to Zone 4; best in warm-winter zones
  • Height and width: Size varies with species; A. calamus grows to 5 feet (1.5m) tall and 24 inches (60cm) wide; A. gramineus grow 3 to 14 inches (8-35cm) tall and 4 to 6 inches wide.
  • Foliage: Clumps of strap-shaped or grasslike foliage that resemble miniature tufts of iris.
  • Flowers: Flowers are inconspicuous and insignificant rounded or club-shaped; flowers are brownish green or white and jut out just below the tops of leaflike flower stalks.
  • Bloom time: Midsummer
  • Uses: Excellent foliage plant for shallow margins of pools, bog garden, or marshy areas.
  • Common name: Sweet flag
  • Botanical name: Acorus
  • Family name:  Araceae 
  • Origin: Native to Japan, northern Asia.

Where to plant Acorus

  • Plant Acorus in full sun or partial shade.
  • Plant Acorus in constantly moist or wet soil that is rich in organic matter.
  • Acorus will grow in standing water.
Acorus gramineus
Acorus gramineus

When to plant Acorus

  • Set Acorus outdoors in the garden in spring or autumn.

Planting and spacing Acorus

  • Space Acorus 6 to 24 inches (15-60cm) apart.

How to water and feed Acorus

  • Acorus want wet or very moist soil. Acorus thrives in shallow standing water.
  • Fertilize Acorus with an all-purpose, liquid fertilizer in spring.

Acorus care

  • Acorus spread steadily but generally aren’t invasive.

Growing Acorus as a houseplant

  • Acorus gramineus is grown as a houseplant; grows 6 to 24 inches tall; ‘Variegatus’ has white-striped green leaves and grows to 12 inches tall.
  • Give Acorus bright light, medium humidity, and a cool temperature.
  • Keep the soil evenly moist to wet; if the soil dries out leaf tips will brown.
  • Misting is not necessary.
  • Check the soil daily for adequate moisture.
  • Fertilize regularly in spring and summer.

Acorus pests and diseases

  • Acorus is suceptible to wet and dry root rots as well as rust and several fungal leaf spots.
  • Acorus can be damaged by red spider mites, especially in a hot, dry environment.

Acorus propagation

  • Propagate Acorus by division in spring. Divide rhizomes at the beginning of the growing season. Pot division up and replant them once they are established.
  • Divide Acorus every 3 to 4 years to keep the clumps vigorous and to contain their spread.

Acorus varieties to grow

  • Acorus calamus. Sweet flag, Sweet calamus. Deciduous species grows to 5 feet tall and 2 feet wide; strap-shaped leaves are ¾-inch-wide. ‘Variegatus’ bears leaves striped lengthwise with cream and white. Plants grow with up to 6 inches of standing water over the rhizomes. Zones 4 to 11 
  • A. gramineus. Grassy-leaves sweet flag. Evergreen to semievergreen species with glossy, linear, grasslike leaves that form arching clumps to about 12 inches tall and wide. Plants grow with 1 to 2 inches of standing water over the rhizomes. Variegated and dwarf cultivars are available. Cultivars include: ‘Ogon’ has rich golden yellow leaves. ‘Pusillus’ is tiny, its green leaves seldom more than 1 inch long; used in miniature landscapes and dish gardens. ‘Veriegatus’, with white-edged, ¼-inch-wide leaves to 1 ½ feet long.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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