Wasabia japonica Seeds | Wasabi
LATIN NAME: Wasabia japonica
COMMON NAME: Wasabi
Plant Profile
Wasabi is an evergreen perennial of the cabbage family with a thick green rhizome, long-stalked heart-shaped leaves and small white flowers in spring. It grows in the gravel of cold mountain streams in Japan, with its roots in running water and its leaves in shade.
The plant is cultivated in terraced beds fed by a constant flow of water at ten to fifteen degrees, in the mountains of Shizuoka and Nagano. It is one of the most valuable crops per hectare in Japan, and one of the most difficult to grow anywhere else. The Japanese name, wasabi, is written with characters that mean mountain hollyhock, a reference to the plant’s habit rather than to its taste.
Science & Biotechnology
The heat is not a capsaicin or a piperine. It comes from allyl isothiocyanate, produced when the cell contents mix on grating: the enzyme myrosinase converts sinigrin into the volatile irritant. That reaction is why real wasabi loses its heat within fifteen minutes on the plate, and why the paste sold in tubes is mostly horseradish with colouring.
The plant needs moving water because its roots require oxygen and its crown rots in still water. The terraces are built on a slope so that water flows through the gravel continuously, and the temperature of that water matters more than the air temperature: above twenty degrees the plant yellows and the rhizome loses quality.
Uses & Benefits
The rhizome is grated fresh onto sushi and into noodle dishes, and the leaves and stems are eaten as a vegetable in Japan, pickled or stir-fried. The grated root is also used in dressings and in a mayonnaise-style sauce.
The leaves are sold as wasabi greens and taste of the same mustard oil at lower strength. In the market, the real rhizome is sold by weight at a price that makes the tube product look cheap, and the difference is worth knowing when a recipe depends on the heat. The grated root is also mixed with soy sauce for a dipping sauce, and the stems are pickled in sake lees.
Growing from Seed
Wasabi is grown from offsets rather than seed, since seed is scarce and slow. Plant the offsets in a gravel bed with water running through it at ten to fifteen degrees, in deep shade. A garden hose trickling through a raised bed lined with gravel can work if the water stays cold.
The rhizome takes eighteen to twenty-four months to reach harvest size, and it is lifted when the crown is five centimetres across. Keep the bed free of silt, since the roots suffocate under mud. In a warm climate the plant survives only with chilled water, and a heatwave can kill a bed in a week.
Our Take
A crop for a cold stream and a lot of patience, and one whose real flavour lasts fifteen minutes. Grow it only if you can keep the water cold.
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