Eutrema japonicum Seeds | Wasabi
LATIN NAME: Eutrema japonicum
COMMON NAME: Wasabi
Plant Profile
Wasabi is a low perennial of the cabbage family from the cool, shaded stream banks of the Japanese mountains, growing about thirty centimetres high with broad, glossy, heart-shaped leaves held on long stalks. In spring it carries small white four-petalled flowers in loose sprays, and the prize is the thick green rhizome at the soil surface, which takes eighteen months to two years to size up.
It is a plant of very particular conditions: shade, cool air, and water moving constantly past the roots at ten to eighteen degrees. Growing it well is a craft, not a formula, which is part of why genuine wasabi commands its price.
Science & Biotechnology
The rhizome’s pungency comes from isothiocyanates, released when the tissue is grated and the enzyme myrosinase meets its substrate, the same chemistry as mustard and horseradish; those compounds have been studied for antimicrobial and possible anti-inflammatory effects.
Because seed is rarely the trade route, most commercial work involves tissue culture and clonal propagation, and the plant’s exacting water chemistry has been a research subject in its own right across Japanese and New Zealand cultivators. Agronomic studies by Japanese and New Zealand growers have quantified the water temperature window and shading levels that produce market-grade rhizomes, turning folk craft into measured practice. The plant’s genetics have been mapped with molecular markers to distinguish true cultivars from seedlings, since genuine wasabi is propagated clonally and much seed-raised stock sold as wasabi is actually horseradish hybrids.
Uses & Benefits
Fresh-grated genuine wasabi is a rare culinary treasure; the heat is volatile and fades within minutes, which is why the rhizome is grated at the table and why the green paste of most restaurants is horseradish with colouring.
In the garden it is a jewel for the shaded water feature: glossy leaves, white spring flowers, and the satisfaction of a plant most gardeners never attempt. Leaves and stalks are pickled in Japan, so little of the plant goes to waste. In Japan the stems and flower stalks are blanched and eaten as a spring vegetable, and grated stems serve as a milder condiment when rhizomes are scarce. Authentic wasabi farms in Japan and New Zealand now sell rhizomes worldwide, and the plant’s scarcity in the market reflects how few growers can meet its water requirements.
Growing from Seed
Seed loses viability quickly and needs no heavy treatment, but it must have cool shade from the start: sow on the surface of a loose, moisture-retentive compost, keep it at fifteen to twenty degrees and never let it dry.
Grow the seedlings in shade with steady, cool moisture, ideally a position beside running or dripping water, and pot them on gently. Plant out only where shade, cool air and moving water meet; elsewhere it stays a pot plant. Mulch the surface with fine gravel to keep the crown cool and moist, and watch for slugs, which find the succulent leaves as attractive as any hosta. Repot every second year and divide old crowns in early spring; each division with a growing point becomes a new plant, which is how the commercial clone lines are maintained.
Our Take
A mountain stream plant with a famous root and no tolerance for shortcuts. Cool shade, moving water and eighteen months of patience: that is the whole recipe.
Related Reading
Gardeners who grow Wasabi often pair it with these related subjects: