Eutrema japonicum
Wasabi
Japan, Sakhalin, and the Korean Peninsula
Overview
Eutrema japonicum is a herbaceous perennial forming a rosette 12-18 inches (30-45 cm) tall and 12-24 inches (30-60 cm) wide from a thickened green stem, or rhizome, that rises above the soil surface as it lengthens. The rhizome reaches 4-8 inches (10-20 cm) long and 1-2 inches (2.5-5 cm) in diameter after 18-24 months and is ringed with raised leaf scars. Leaves are long-petioled with heart-shaped to kidney-shaped blades 4-8 inches (10-20 cm) across, glossy dark green and toothed along the margin, on petioles 8-14 inches (20-35 cm) long. White four-petalled flowers 0.3-0.5 inch (8-12 mm) across open in racemes held 8-16 inches (20-40 cm) above the foliage in spring, followed by slender siliques 0.6-1 inch (1.5-2.5 cm) long. Growth stalls above 80F (27C) and leaves scorch and rot in still, warm air. Plants grow in flowing water at 46-59F (8-15C) under stream culture, and in shaded, constantly moist soil under field culture, where rhizome diameter runs 30-50% smaller. Pungency comes from allyl isothiocyanate released when rhizome cells rupture, and the compound breaks down within 15-20 minutes of grating.
Native Range
Eutrema japonicum grows wild along cold mountain streams and seepage slopes on Honshu, Shikoku, and Kyushu in Japan at 600-4,600 feet (180-1,400 m) elevation. Populations also occur on Sakhalin and in parts of the Korean Peninsula. Wild stands sit in shaded ravines under deciduous forest where water stays between 46 and 59F (8 and 15C) year-round.Suggested Uses
Grown in shaded stream beds and gravel raceways at 8-12 inch (20-30 cm) spacing for rhizome production, and in shaded soil beds at 12 inch (30 cm) spacing where flowing water is unavailable. Container culture uses pots of 5 gallons (19 L) or larger in a shaded, humid position with daily watering; container rhizomes run 1-1.5 inches (2.5-4 cm) thick against 1.5-2 inches (4-5 cm) under stream culture. Leaves, petioles, and flower stems are eaten alongside the rhizome, and the plant is grown as a shaded foliage perennial in woodland gardens in zones 7-9.How to Identify
Appearance
Size & Dimensions
Height1' - 1'6"
Width/Spread1' - 2'
Reaches mature size in approximately 2 years
Bloom Information
Flowering runs March through May in zones 8-9, and April into June at higher elevations and in zone 7. Racemes lengthen over 3-5 weeks, opening from the base upward, and total bloom on a plant lasts 4-6 weeks. Plants flower in their second or third spring. Flowering draws reserves from the rhizome, and stems are cut at the base in commercial culture so rhizome bulk continues to build.
Detailed Descriptions
Foliage Description
dark greenGrowing Conditions
Sun Requirements
Tolerates up to 4 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
Plants take constant moisture with water moving over or through the root zone, and stream culture holds water at 46-59F (8-15C) with continuous flow. In soil culture, beds stay evenly moist under 50-75% shade cloth with irrigation two to four times daily in summer. The gravel or soil medium drains freely while staying wet, since standing anaerobic water triggers soft rot caused by Pectobacterium carotovorum. Air temperatures above 80F (27C) for more than a few days cause leaf scorch, and prolonged heat kills plants outright. Blackleg caused by Phoma wasabiae and Verticillium spp. wilt spread through infected planting stock, and aphids colonise leaf undersides in spring. Rhizomes reach harvest size in 18-24 months, after which beds are replanted from offsets rather than held a third year.Pruning
Outer leaves yellow from the base through the season and are removed at the petiole base as they decline, which limits soft rot in the crown. Flower stems are cut at the base as they emerge in commercial culture, since seed production reduces rhizome bulk by 20-30%. Offsets forming around the main rhizome are separated at harvest and used as planting stock. No structural pruning applies.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
late springsummer
Container Growing
✓ Suitable for container growing
Minimum container size: 5 gallons