Acorus calamus
Sweet flag
Common names: European sweet flag
At a glance
- Light
- Full sun
- Spacing
- 40 cm, rows 50 cm
- Lifespan
- Perennial
- Planting
- Apr–May
- Harvest
- Sep–Oct
- Hardiness
- Hardy down to −20 °C
- Water need
- High
Photo: J.F. Gaffard, Autoreille, France · CC BY-SA 3.0 · Source
This description was machine-translated.
Description
The sweet flag is a reed‑like riparian plant with sword‑shaped, aromatic leaves, botanically Acorus calamus. In nature it grows in the shallow water zone of ponds and ditches, where its creeping rhizome forms dense clumps. For centuries it was valued as a spice and medicinal plant; today it is prized mainly for its aroma and its effect as a pond scenery. The sweet flag is not suitable for consumption.
Care instructions
Plant the sweet flag in the shallow water zone of your pond, in a planting basket with loamy, nutrient‑rich soil, about 5 to 15 cm below the water surface. It tolerates full sun to partial shade and requires permanently moist to wet soil; never let it dry out. In late autumn, remove the wilted leaves; leave the rhizome to overwinter in the water; it is hardy down to well below freezing. Every three to four years, divide the clump in spring, once the first shoots become visible from mid‑April (week 16), to keep the plant vital and prevent uncontrolled spread.
The care notes were machine-translated from German.
Garden year
PlantingApr–May
HarvestSep–Oct
Soil & site
Soil pH
Soil type
moist, humus-rich, nutrient-rich, loamy
Sweet flag likes to grow with its feet in the water, right at the edge of a pond or stream, where the soil stays permanently moist to wet. A muddy, nutrient-rich ground comes closest to its natural habitat in marsh and bank. It shrugs off short floods without trouble, but the soil should never dry out completely.
Feeding
Medium feeder
Months
Apr–Jun
In spring and early summer, sweet flag appreciates a helping of well-rotted compost worked into the moist substrate. Near ponds, the natural nutrient input from the water is often enough. If you do fertilise additionally, use organic material that acts slowly and does not burden the water.
Overwintering
Sweet flag is hardy and survives the cold season outdoors at the pond edge without special protection. The rhizome overwinters below the water or soil surface, while the leaves above ground die back in autumn and can be cut back. In containers at the bank, a layer of leaves or mulch over the root zone helps to stop the rhizome freezing through.
Propagation
Methods
- Division
The simplest and most reliable method is division of the rhizome in spring, as soon as new shoots become visible. Dig up the rootstock and separate strong pieces with at least one growth bud. Set the divisions straight back into moist soil or in shallow water, and they quickly form new leaves. Since sweet flag usually flowers sterile in Central Europe, sowing plays hardly any role in propagation in the garden.
For your garden
Grow Sweet flag yourself
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