Wasabi growing in gravel beds flooded with spring water
Wasabi prefers cool, shady conditions and will sometimes thrive if left undisturbed in misty mountain stream beds. It generally requires a climate with an air temperature between 8°C (46°F) and 20 °C (70°F), and prefers high humidity in summer. Since it is quite intolerant of direct sunlight, wasabi is typically grown under shade cloth or beneath a natural forest canopy.
Wasabia japonica grows in northern Japan, parts of China, Taiwan, Korea and New Zealand. In North America, the rain forests found on the Oregon Coast and in parts of the Blue Ridge Mountains in North Carolina and Tenessee provide just the right balance of climate, sunlight and water quality to grow natural wasabi. Limited success has been achieved by firms using greenhouse and/or hydroponic techniques, but the resulting costs are typically quite high. In Japan, the highest prices are paid for all natural, water grown "sawa" wasabi.
Wasabia japonica plants are slow growing perennials with a rooted, thickened stem (rhizome), long petioles and large leaves. All parts of the wasabi japonica plant, including rhizomes, roots, stems and leaves are harvested, processed and valued for use. The rhizome serves as storage for the plant’s nutrients (similar to a potatoe) and is where the flavors tend to be most concentrated. The appearance of the wasabi rhizome is similar to a brussel sprout stalk after the sprouts are removed. The long stems (petioles) of the Wasabia Japonica plant emerge from the rhizome to grow to a length of 12 to 18 inches and can reach a diameter of up to 40 mm (1 ½ in). They terminate into single heart shaped leaves that, in optimum conditions, can reach the size of a small dinner plate.
Wasabia japonoica plants can take as much as three years to reach maturity. Initially, given the right conditions, the wasabi plant produces robust top and root growth, reaching approximate knee height (2 feet) with an overall width about the same. After this initial establishment phase the rhizome begins to build and store reproductive nutrients. It is this concentration of energy which produces the best flavors so the rhizomes are generally the most valued for culinary purposes. Typically the rhizome will reach a size of six to eight inches long and an inch or so in diameter in approximately twenty four months.
Wasabi leaves and leaf stems (petioles) tend to be brittle. Breakage or damage from animals, field workers or mishandling can cause growth to slow and sometimes even stop for short periods of time.
Under optimum conditions, Wasabia japonica will reproduce itself by seed. In commercial wasabi farms, plant stock is typically extended by replanting small offshoots which characteristically occur as the plant matures.