Flax lilies (Dianella spp.) and sweet flags (Acorus spp.) Resemble each other superficially because both have a somewhat grasslike aspect with clumping growth. They differ from each other in most other elements, however, and aren’t closely associated. Flax lilies are grouped with lilies, with 15 flax lily species native to Australia and Tasmania. Tasmanian flax lily (Dianella tasmanica) is commonly grown in North America. Sweet flags are from the arum or Araceae family, with two to six species occurring in Europe, North America and Asia, plus some garden cultivars. The sweet flags within the United States are mostly sweet flag calamus (Acorus calamus). Tasmanian flax lily is suitable for dry habitats and sweet flag calamus for moist to aquatic habitats.
Leaves and Growth Habits
Tasmanian flax lily’s 1- to 2-foot-long leaves are green to blue-green and about 1 inch wide. The plant usually grows about 2 feet tall but can reach 3 feet high with a width of about 2 feet. Sweet flag calamus’ bright-green leaves are about 3/4 inch wide and have a sweet scent. That plant grows 3 feet tall and wide. Both plant species have a comparable, straplike leaf growth pattern. Both also have variegated forms. Variegated Tasmanian flax lily (Dianella tasmanica “Variegata”) has yellow stripes down the outside borders of every leaf. Broader, cream-colored, longitudinal stripes characterize variegated sweet flag calamus (Acorus calamus “Variegatus”).
Tasmanian flax lily has an open, branched flower stalk that rises above the foliage and bears little, six-petaled, inconspicuous, bluish flowers that could appear throughout the year. Removing the spent flower stalks occasionally gives the plant a tidier look. Sweet flag calamus bears its tiny, greenish blooms on a specialized rod-shaped structure called a spadix, that is 2 to 4 inches long. The plant blooms from May to July.
Well-drained soil is ideal for Tasmanian flax lily, which can withstand some periods of drought. When grown in a container, the plant requires regular watering. Whether grown in a container or inground garden, nevertheless, enable the plant’s top 1 to 2 inches of soil to dry out before watering the soil again. Sweet flag calamus, on the other hand, requires always moist soil and can succeed in up to 9 inches of standing water. Grow it in a marshy or boggy place, shallow garden pond or other water garden.
Tasmanian flax lily is best suited for a place with warm winters; it is hardy in U.S. Department of Agriculture plant hardiness zones 8 or 9 through 11. Variegated Tasmanian flax lily is hardy in USDA zones 8 through 10. The leaves of the plants can die back during cold winters. Sweet flag calamus is hardy in USDA zones 4 through 11, and variegated sweet flag calamus is perennial in USDA zones 4 through 8. In areas with cool summers, the two Tasmanian flax lily and sweet flag calamus do well in sunlight. In hot-summer areas, both species, and especially the variegated cultivars, benefit from partial shade. Tasmanian flax lily grows gradually while sweet flag calamus can grow rapidly. In favorable conditions, sweet flag calamus could spread, naturalizing into non-garden areas where conditions allow. If you do not need sweet flag calamus to spread, then maintain its rhizomes in a container that you sink in the ground.