Richters InfoSheet D6720
In Japan wasabi is grown in beds of sand or gravel through which water is constantly flowing. The cost of building and maintaining these beds contributes to the high cost of wasabi in the market place. In other areas of the world, notably China and Taiwan, wasabi is grown very successfully in soil. Wasabi grown in soil commands a lesser price in the market but is not necessarily of any lesser quality or inferior taste.
Most wasabi originates as small plantlets or divisions growing around the central rhizome of the mature wasabi plants. A large plant may have upwards of 10 plantlets which can be derived from the mother plant at time of harvest. It is claimed that after several generations of divisions that stock must be renewed either from seed or through micropropagation to eliminate diseases which have accumulated in the plant stock. So far this has not been our experience. Seeds are extremely small and must undergo a period of cold storage before they become viable. We have not yet attempted culture from seeds.
Our plants are grown in straight compost under 70% shade cloth. During summer the foliage is sprayed liberally with water once or twice per day so that soil moisture and humidity remains relatively high in the growing area. After 18 months to two years the plants are harvested and divided. Usually this should occur in the late spring or early summer after the plants have fully recovered from their winter dormancy and produced a full set of new large leaves.
In mild areas such as the Seattle area wasabi passes the winter without much problem. When the weather begins to go below freezing at night, the plants are covered with a sheet of clear plastic. In area of the country where temperatures regularly fall to -5°C (20°F) or below we suggest that the plants may need to be moved indoors or at least heavily mulched and then protected by some type of fabric or plastic covering.
When your plants arrive soak the roots thoroughly and then plant in loose moist soil in an area which receives indirect sunlight. Avoid high temperatures and mist the plants daily to keep humidity up. If the leaves wilt completely (which is not unlikely) cut them off after you are sure they will not revive. This will keep the old leaves from leaching too much moisture away from the central rhizome. Then let the plant regenerate new leaves from the base.
Wasabi will only tolerate a limited amount of direct sunlight. If your plants seem to wilt during part of the day they are receiving too much sun. If the leaf color lightens or begins to take on a slightly yellow hue they are also receiving too much light. Watering the plants to cool and hydrate them will allow them to pass through limited periods of direct sunlight. Soil should be high in organic matter. Cover the roots of the plant up to the base of the lowest stems. Water the plants thoroughly. Leaves and stems that appear wilted should rehydate and perk up. If you find that some stems remain wilted for two or three days, remove them. In a few days you should notice the appearance of new leaves. Be sure to protect the plants from predators, particularly slugs and snails. Any metaldehyde type slug bait should do to protect the plants.
A couple of times a year you may want to apply fertilizer, any good vegetable fertilizer should do. Addition of sulfur to the soil will increase the pungency of the plants’ taste.
When the central rhizome (both above and below the ground) reaches 10-15 cm (4-6 inches) and 1-2 cm (0.5-1.0 inch) in diameter, the plants are ready to harvest. Pull the plants up and remove the plantlets around the rhizome for replanting. Wash the plants thoroughly and remove any dead or dying leaves. Break off all roots flush with the rhizome. Remove and retain the stems and leaves. Use a carrot peeler to shave off the outer layer of the rhizome. Use a fine grater to grate the central portion of the rhizome and serve it with sushi or sashimi, or steak for that matter. For increased volume the leaves and stems may also be pureed into the preparation. Commercial wasabi available in Oriental groceries is mixed with horseradish. You can try this mixture also. Grated wasabi will not retain its flavor for very long. Even storage overnight in the refrigerator will cause the paste to lose virtually all ofits flavor. Addition of preservatives will likely increase the shelf life of the paste but we have not tried it.
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D6720 ©2004 Otto Richter and Sons Limited