Acorus calamus

Acorus calamus, also known as Sweet Flag, Reed or Sweet Sedge, is a semi-aquatic perennial plant with a grass-like appearance, distinguished by its elegant, graphic foliage, semi-evergreen, aromatic when crushed. Its long, narrow, bright green ribbon-like leaves emit a mandarin scent. This species, naturalized in the northern hemisphere, is widely used in herbal medicine. Hardy, it can be planted in heavy, moist soil or in shallow water, where it may eventually produce insignificant flowers. Acorus brings brightness and structure to the edges of water features or in wet areas, in full sun or partial shade.

Acorus calamus belongs to the Araceae family. Native to Asia, it can be found in Northern and Central Europe, as well as North America. In eastern France, it has adapted to the edges of ponds and ditches. The Sweet Flag grows from a trailing, ramified, vigorous rhizome, which thrives in permanently moist soil, even in shallow water. With an upright habit, the plant reaches a height of 80cm (32in), or even 1m and more. Its leaves are sheathing, basal, ribbon-like, narrow, bright green, with plicate margins. They form large clumps. The young spring shoots have a reddish colouration. They are fragrant when crushed. Its insignificant flowers appear in summer if the plant is submerged, in a cylindrical yellowish spike of about 7cm (3in) long. Acorus calamus is the hardiest of the Sweet Flags, tolerating temperatures of around -15 to -20°C (5 to 1°F), once well established. It is more sensitive to cold in its youth. 

Acorus calamus is a good choice for planting at the edge of a water feature or in a wet area, in wild or contemporary gardens. Pair it with Astilbes, Carex, Rodgersias or Filipendulas. Growing it in a large container, such as a zinc tub, also allows for the creation of a successful mini-aquatic garden by combining it with two or three shallow-water plants of contrasting shapes and colours, such as Cyperus papyrus 'Akhenaton'.

The dried rhizome has medicinal properties still used in parapharmacy and herbal medicine.