Acorus gramineus
Japanese sweet flag
Japan, Korea, China, India, Southeast Asia
Overview
Acorus gramineus is a rhizomatous perennial forming fans of narrow grass-like leaves 6-12 inches (15-30 cm) tall, with clumps widening to 12-18 inches (30-45 cm) over 3-4 years. Leaves are linear, 0.2-0.5 inch (5-12 mm) wide, glossy, and set in flattened fans from a creeping rhizome at or just below the soil surface; crushed foliage carries a sweet spicy scent. The plant is not a grass and sits in the family Acoraceae, with leaf fans in place of jointed round stems. Flowers are carried on a greenish-yellow spadix 1-4 inches (2.5-10 cm) long in late spring, without a coloured spathe. Cultivars carry gold foliage in Ogon, cream stripes in Variegatus, and a dwarf habit at 3-4 inches (8-10 cm) in Pusillus. Growth continues in soil that stays wet, on bog margins, and in standing water to 4 inches (10 cm) deep, while leaf tips brown within days if the root zone dries out. Rhizomes contain beta-asarone, a compound restricted in food use in the European Union. Plants come through winter to -20F (-29C), holding their leaves in mild regions and dying back to the rhizome in USDA zones 5-6.
Native Range
Acorus gramineus is native to Japan, Korea, China, India, and Southeast Asia, where it grows on stream banks, in wet woodland, and on rocks in running water below 8,200 feet (2,500 m). It has been cultivated in Japan and China for centuries, in gardens and in traditional medicine, and reached European horticulture in the 18th century. It is planted through temperate and subtropical regions in USDA zones 5-9.Suggested Uses
Planted at 8-12 inch (20-30 cm) spacing along pond margins, in rain gardens, in damp shade, and between paving across USDA zones 5-9, where the fans hold their outline through the season. Grown in containers of 3 gallons (11 L) or larger standing in water, and in bowls indoors in bright light. The dwarf cultivar Pusillus at 3-4 inches (8-10 cm) is sold for planted aquariums, where it grows in shallow water rather than fully submerged over long periods.How to Identify
Appearance
Size & Dimensions
Height6" - 1'
Width/Spread1' - 1'6"
Reaches mature size in approximately 3 years
Bloom Information
Flowering runs 2-3 weeks between April and June, with the spadix standing 1-4 inches (2.5-10 cm) long at an angle from the flowering stalk. Flowers are greenish-yellow and 0.1 inch (2-3 mm) across, packed along the spadix without a coloured spathe. Fruit rarely forms on plants in cultivation, and spread runs through the rhizome at 2-4 inches (5-10 cm) per year. Cultivars grown for foliage flower sparsely or not at all.
Detailed Descriptions
Foliage Description
Glossy mid green; gold on Ogon and cream-striped on VariegatusGrowing Conditions
Sun Requirements
Requires 2-8 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Growth continues from full sun through half shade, with gold and variegated cultivars holding colour in 4-6 hours of morning sun and scorching in full afternoon sun above 90F (32C). Soil that stays wet at pH 5.5-7.5 suits the roots, including pond margins and standing water to 4 inches (10 cm) deep. Plants in ordinary borders take 1-2 inches (25-50 mm) of water per week, and leaf tips brown within days of the root zone drying out. Fertilizer is generally unnecessary in rich wet ground, and a slow-release feed in spring covers container plantings. Few pests occur, while crowded clumps in still water develop crown rot. Foliage holds through winter in USDA zones 7-9 and dies back to the rhizome in zones 5-6, regrowing in April.Pruning
Old and browned leaves are combed out by hand or cut back to 2 inches (5 cm) in early spring, before the new fans push. Cutting the foliage in autumn removes the winter cover in mild regions, where the leaves stay green. Clumps are lifted and divided every 3-4 years, with the rhizome cut into sections carrying 3-5 fans each. Divisions replanted with the rhizome at soil level establish within 6-8 weeks in warm weather.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
early spring
Container Growing
✓ Suitable for container growing
Minimum container size: 3 gallons