Have you ever tried that dob of green paste that comes with sushi and sashimi? Did you know that the green paste sold as wasabi in the supermarket is actually horseradish that’s been dyed green? Yes it’s got plenty of bite but it’s not wasabi, which is sweeter tasting. While you only need ¼ of a teaspoon of the stuff to get steam coming out of your ears, water running out of your eyes, and the feeling that your nose is going to lift off into space, true wasabi doesn’t have the lingering super-hot after-burn of the inferior substitute.
Wasabi is Eutrema japonica, (syn Wasabia japonica – renamed in 2010), and it’s a semi-aquatic brassica plant that grows wild in Japan and is related to horse radish, Armoracia rusticana. Wasabi grows naturally alongside mountain streams in areas of low light, low temperatures and high humidity. It’s a herbaceous perennial plant with a thick knobbly rhizome about 10-30cm long and about 2-5 cm thick. It’s the rhizome that is grated to form wasabi. But real wasabi is very hard to come buy, fearfully expensive (about $100/rhizome) and doesn’t keep for long so why not grow your own local supply so you can keep on grating it fresh?
Wasabi prefers a cool temperatures between 8°C (46°F) and 15 °C (60°F) and very moist, shady positions. In Japan there are about 20 cultivars but outside Japan you will probably only find either ‘Daruma’ or ‘Mazuma’ for sale. Commercial growing in Japan is on sloped gravel beds covered with a layer of sand over which flows a thin layer of cool water. Ideally you’d would grow wasabi in your own cool, mountain stream but unfortunately not many of us have one flowing through our yard. The next best alternative is somewhere very cool and damp, with about 80% shade and high humidity, like you’d find in a fernery. Prepare the soil with plenty of organic matter and keep the plants well-watered but not saturated – they’ll still need good drainage or they’ll get root rot. Apparently there’s not much difference in taste between the water grown or soil grown wasabi.
As you’ll probably be buying your wasabi mail order, keep it wrapped in damp newspaper and in a cold, moist place until you’re ready to plant it. You can either get it growing in a small pot first or put it straight in the ground. Dig a hole twice as wide and deep as the roots, then insert the plant with the roots gently spread out and with the base of the leaf stalks slightly above the soil surface. Backfill with soil and gently press into place. Water it in well and don’t fertilise until you see some growth. You could also try growing it along the margins of a backyard pond, as long as it’s well shaded.
Newer commercial ventures are growing wasabi hydroponically in green houses but there’s still a lot of experimentation going on to get the conditions just right.
Your new wasabi plant is unlikely to produce new growth for several weeks, due to the stress of transport. If planted in summer or winter they may not produce new growth at all until the following autumn or spring. If it does grow after a few weeks, to concentrate growth in the rhizome and plant itself, break off any suckers that form. Protect your plant from slugs and snails, as well as white cabbage butterfly and aphids, and cover it in frosty conditions.
You can also grow it in a container (try one about 25cm diameter/9li/2.5 gal) or foam box in either water-covered gravel or moist soil and cover it with 75% shade-cloth if you don’t have a shady spot in the garden. Remember if you use soil to punch some holes in the foam box for drainage.
Unless you have cold conditions, your wasabi is unlikely to flower or set viable seeds. Seeds are also very difficult to germinate but you could try some artificial stratification by refrigerating them in a glass jar for a few months and sowing them in late winter in a perlite-vermiculite mix that’s kept very moist.
Wasabi will need to grow for about 18 months to 2 years before the rhizome is a sufficient size (50gm) for harvesting. A mature plant is about 40cm tall and can live for many years. However while you’re waiting for the plant to mature, you can use the leaf and stem in salads and stir fries adding a delicious mild wasabi ‘zing’. The leaves can be pickled in sake, brine or soy sauce and can even be powdered for use as wasabi flavouring.
Harvesting is done in autumn (fall) or spring when it’s cool and moist. As you harvest, you can cut off the small plantlets that have developed alongside the main rhizome and plant them as your next crop.
When eaten raw, the wasabi rhizome is washed and trimmed of outer bumps and then grated. Carefully scrub off all the dirt (soil isn’t that tasty!)
Grating, according to Japanese tradition, has to be just right. The wasabi cells need to be torn apart to set off a chemical reaction, which after a few moments rest, develops its ‘wow’ flavour. You need just that right type of very fine grater, so you can’t use a nutmeg grater because it’s too coarse and slices instead of grinding. The graters are called oroshigane. These oroshigane graters have fine teeth on one side for wasabi, and coarse on the other for ginger and daikon.
You can also buy much cheaper plastic versions of this grater.
The next trick is that you have to hold the rhizome at 45 degrees and use a circular motion with your wasabi on its special grater.
The Japanese consider wasabi a gourmet treat, and it’s used in a wide range of foods and drinks. Apart from clearing out your sinuses, wasabi has a few health benefits too as it’s high in vitamin C, dietary fibre and potassium, with some calcium and protein. Wasabi kills food borne bacteria and reduces blood pressure, plus there are anecdotal reports of its anti-cancer properties, but that’s not medically tested.
Where to buy wasabi plants
You can buy the rhizome to grow some of your own, from mail order catalogue or online, or wasabi is sometimes available as seed or tissue culture.
Australia – Four Seasons Herbs, Rubicon Mountain (03) 5773 2200 or 0409 042 858. Diggers Club will often have Daruma in autumn, which copes better with warmer conditions, has a superior green colour, size and crisp taste, and produces a better quality stem (used extensively in salads) and generally has a more attractive appearance. The Mazuma variety grows to only 40cm and needs to be grown in complete shade.