Acorus gramineus goes by many common names like: Japanese Sweet Flag, Japanese Rush, and Grassy-leaved Sweet Flag. It belongs to the genus Acorus, and now has its own family group (Acoraceae), although it used to be classified as part of the Arum family. It is native to eastern Asia, specifically China, Japan, Korea, India, Thailand, Myanmar, and the Philippines, where it favours growing in wetlands and shallow water.
This attractive, grass-like little plant only grows about 30cm in height and the long, narrow green leaves grow in flattened fans like those of irises, crowded along short rhizomes (roots). Both the leaves and rhizomes emit a sweet citrus scent when crushed or bruised, hence the common name sweet flag. Tiny, insignificant, yellow-green flowers appear from spring to early summer on lateral flower spikes (spadixes), and give way to very tiny, fleshy, reddish berries.
Acorus gramineus ‘Golden Edge’ has slightly curved foliage that ranges in colour from light to golden yellow, and is striped with green. The tussocks, or clumps, grow to about 30cm tall and wide.
Acorus gramineus ‘Variegatus’ grows about 25 to 30cm tall and wide, forming a low mound of narrow sword-shaped leaves, striped lengthwise with green and creamy-white.
Acorus gramineus ‘Mini-Gold’ is a cheeky looking little dwarf with yellow and gold leaves and an adult size of around 15cm tall and wide.
Acorus gramineus 'Liquorice' is known as “Sekisho” in Japan where the liquorice flavour of the rhizomes and leaves are used in cooking. The rhizomes are roasted or stir-fried, and the leaves are cooked with rice. It is also used medicinally, and especially in Chinese medicine, as an antibacterial tonic herb, for indigestion, to stimulate the digestive system, for flatulence, stomach cramps, chronic dysentery, to clear the bronchial passages and to strengthen the nervous system.
Acorus calamus is worth mentioning here as it is a popular garden species associated with wetlands throughout Eurasia and eastern North America. It has green iris-like leaves up to 1.5m long, and a narrow 10cm long elliptical green spadix (a fleshy spike bearing small flowers). Its stout, aromatic rhizomes contain compounds that are still used in herbal medicines, and sometimes for perfume. Acorus calamus 'Variegatus' has cream and yellow variegated leaves.
In Japan during the Heian period, leaves of Acorus calamus were gathered for the Sweet Flag Festival, held annually on the fifth day of the fifth month. Sweet flag and wormwood were spread on the roofs of houses for decoration and to ward off evil spirits, and special herbal balls made of sweet flag were also fashioned for the occasion.
Acorus gramineus 'Ogon' Picture courtesy K M from flickrIn the Garden:
Acorus are just as happy growing in water or a bog situation as they are growing in ordinary garden beds, and they can be sited in sun or semi-shade to shade. And although they are not grasses, they are planted to create the same effect in the garden as ornamental grasses would.
Because they love water they can be planted into pots and placed in water with the rim just above the water line, so use sweet flag in water features and ponds to create a more natural environment and to provide protection for freshwater aquatic life. Never plant exotic plants near to our natural dams or streams where they could become invasive; rather restrict them to garden features.
In Japan the smaller cultivars are often grown indoors in large ceramic bowls filled with water, and the plants are especially suitable for miniature water features.
Sweet flags also serve to soften hard lines created by solid concrete edges and rock placements, and are excellent choice to prevent soil erosion on banks and slopes, providing a virtually maintenance free groundcover.
Sweet flags blend in effortlessly with all types of garden styles and are ideal perennials to use as a ground cover, or for mass planting in any landscape, as they grow vigorously, creating a nearly-seamless groundcover where conditions are favourable.
They even grow effortlessly in pots, looking lovely planted on their own or combined with other plants with similar watering needs.
Acorus gramineus 'Ogon' growing alongside a stream in Japanese Friendship Garden. Picture courtesy K M from flickrCultivation/Propagation:
Acorus grows easily virtually throughout South Africa as long as it can be watered regularly. It does not perform well in dry soils and will need regular watering in the garden. This is especially important in the winter rainfall regions and in the drier summer rainfall regions of the country.
The green-leaved Acorus gramineus is fully hardy frost and temperatures down to -15°C, but the golden varieties may get scorched by severe frost, but will quickly shoot again in spring if the roots are well mulched in autumn.
The sweet flag is great in coastal landscapes because it tolerates salt winds with ease, and in these regions it thrives in beds on the shady side of the house.
Even though Acorus will grow in semi-shade and full sun, it does not like intense heat, so in very hot areas plant it where it will receive some shade during the hottest part of the day, or dappled sunlight throughout the day. Dry soils coupled with intense sunlight will scorch the foliage.
The plants will adapt to soils ranging from very acidic (pH 5.2 to 5.5) to alkaline (pH 8.1 to 8.5) and will flourish in most fertile garden soils, even heavy clay. Add generous amounts of compost to the beds before planting to help conserve water, and for a groundcover space the plants about 20 to 30cm apart, depending on the variety grown. Plants can take 2 to 3 years to reach their ultimate height, which may be taller than described, with a wider spread.
Propagation is easily done by digging up and dividing the tussocks at any time of year. Division of the clumps should be done every 3 to 4 years to maintain plant vigour.
Problems, Pests & Diseases:
Insects and diseases are generally not a problem for this plant.
Too much summer sun or protracted dry conditions will cause the plants to look poorly, and scorching of the foliage can arise.
In too much shade growth will be stunted.
Warning:
Although no records of toxicity have been seen for Acorus gramineus, this species belongs to a family where most of the species are poisonous, at least in the fresh state. Always supervise small children in the garden, and discourage pets from chewing on plants.