Wasabi, or Japanese Horseradish (Wasabia japonica (Miq.) Matsum), can probably be considered as green gold these days. Fetching near $250 US per kg, it is very tempting to take on commercially. The effect of the product on the taste buds makes it very interesting to grow personally. The potential uses of the product in a wide range of applications, outside of consumption, from antibiotic to pesticide, make it a plant of the future. The characteristics of the plant make it exceedingly difficult and picky in cultivation.Thoughts on the Plant and Its Cultivation
Wasabi is a perennial aromatic herb growing from a short, thickened stem (rhizome) from which other rhizomes and secondary stems can form. The stems can be separated for propagation as well as the rhizomes. The plants are grown for their rhizomes, leaves and petioles, but it is the rhizome that is the most valued part of the plant which is grated and turned into pastes and other food preparations. The leaves and petioles are pickled in sake brine or soya sauce as a side dish; leaves are used fresh in salads or dried for use in flavoring dishes. Lower quality stems are mixed with European Horseradish (Armoracia rusticana) and turned into a wasabi paste.
The key to the special taste of Wasabi is in the content of Isothiocyanates (ITC’s). These are not present in the plant tissue but evolve from a similar group of compounds known as Glucosinolates (GSL) and are produced when the tissue is disrupted by grating, chewing, cutting, etc. They evolve quickly but are very volatile which means they disburse quickly as well. Wasabi has a sting to it but not like peppers, this sting goes away quickly. This is why the rhizome is preferred and why it is best prepared and used at the same time.
So why is it not a plant for beginners? Specialized cultivation; that and 18 – 24 months. Wasabi is native to Japan where it grows along the gravel banks of mountain streams and rivers. It has to have two things: water and cool temperatures. There are two types or methods currently used for growing Wasabi: upland or soil, and flooded field or water. Upland is used primarily for growing the leaves and petioles, where as the water method is used to produce the thicker rhizomes. Either method has can be used successfully if the grower can control the environmental variables as this is a 2 year crop requiring extended investments and locked in assets.
The soil method, or upland, requires air temperatures of 6 – 20oC with 8 – 18oC considered optimal. Soils are best at a pH of 6 – 7 and should be very well drained. In the water method, air temperature should be 8 – 18oC but a narrower range, 12 – 15oC is considered optimal. Temperatures of 8oC will inhibit growth and below 5oC growth will stop. Other factors that have to be considered include stable cool water temperatures, water clarity, high dissolved Oxygen content, and good nutrient status at lower solution concentrations. The water flow must be constant and correct.
Both methods require the plants be held at a low light level. (<700 µM m-2s-1) It takes at least 18 months for the crop to reach full maturity. Wasabi is a member of the Brassicaceae family and is subject to attack by various insects (aphids, slugs) and diseases including root and stem rots (Phoma, Botrytis ), bacterial soft rot (Erwinia), and Powdery Mildew. Insect and disease issues will increase with temperature and water issues. Soil based methods have to have ample drainage and irrigation frequency will be high under optimal conditions. Water based systems must be well aerated and moving constantly at low flow rates because with lower EC levels, the nutrients have to be refreshed along with the oxygen.
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The Aqua nutrient line from Canna offers one of the best hydroponic nutrient solutions available for production of Wasabi indoors or out. Its stable pH, nutrient ratio longevity, and clean formulation insure that these consistency standards are maintained. Wasabi is a very light feeder and because of this, it is best to use a very low EC water source to ensure that the EC the plant sees is almost entirely available nutrients. Mechanical agitation, not air injection, is the best way to insure proper oxygenation is maintained in the solution while not affecting the pH buffers in Aqua as much. Still, the grower will have to monitor the pH closely. Aqua will help hold the pH more neutral (7.0) which is where it should be. Keep the water moving; plants will be best produced in gravel/ sand or sand beds using a nutrient flow technique: above everything else, keep it cool.