Marianne CannonHow to grow red hot green wasabi

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.

Wasabia japonica Photo by Qwert1234

Wasabia japonica Photo by Qwert1234

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?


Growing wasabi

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.

Wasabi_IngroundAs 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.

Wasabi_leavesYour 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_stemHarvesting wasabi

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.

Wasabi Photo by kaitea

Wasabi Photo by kaitea

Eating wasabi

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!)

Wasabi_graterGrating, 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.

Wasabi oroshigane Photo Chris 73

Wasabi oroshigane Photo Chris 73

Using wasabi

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.

UK & Europe – The Wasabi CompanySuttons Seeds (in season)

USA – Pacific Coast Wasabi; Frog Eyes Wasabi

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Marianne Cannon

About Marianne Cannon

Marianne Cannon has been broadcasting as Real World Gardener on radio 2RRR 88.5fm in Sydney, since September 2009, and the program is now syndicated to radio stations around Australia. It's about growing your own, the abc of plants, and how to create sustainable gardens to fit into today's environment. Not just a show about plants; it has a strong green and ecological bent, with co-presenters addressing issues such as native animals and plants, water conservation, composting, reducing waste, protecting native species and more.

11 thoughts on “How to grow red hot green wasabi

    • I didn’t think is sounded that bad. There’s always that really shady damp spot in the garden. I’m going to give it a try but will have to wait until May to get the Daruma variety.
      The leaves are also good for wrapping sashimi slices of fish apparently. Might also be a nice substitute for Betel leaves in Asian cooking.

  1. Hi Marianne,
    I was in Japan last year and visited a wasabi farm – corrugated banks of shingle in shallow running water (a stream, as you say). As it was spring the women were picking the green tops for sale and apparently the flowers are also edible.
    We bought some wasabi greens and took them to our hotel where they prepared them for us. The hotel owner’s wife showed us how to prepare the root – the traditional grater is a piece of sharkskin on a wooden tablet.
    We had earlier tried cooked “yellow” wasabi at another traditional hotel, very mild and quite refreshing, while at the farm we bought wasabi ice-cream, but suprisingly that didn’t seem to have much flavour at all (at least to our palate).
    There are some commercial wasabi-growing operations in the South Island of New Zealand, a couple for nutra-ceuticals rather than the condiment.

      • Oh yes, the greens were subtle in their taste, but refreshing, while the real wasabi was nothing like the stuff in tubes. It had heat, certainly, but not anything like unbearable (you know, where you think that it’s avocado and it turns out to be wasabi!).

  2. Can anyone advise where one can get real Wasabi in Sydney? I love the taste and that sense of the nasal passages being cleaned out. But now I find I may have been eating horseradish dyed green! In the many Japanese restaurants in Sydney, when one gets a little sachet of the green stuff, would this usually be the real deal? Could I grow Wasabi in my very shady garden, or is Sydney too hot?

  3. Hi Marianne, I bought wasabi in a pot last year and I have grown it in a polystyrene box in a very shady spot. I slosh over a bucket of water at least once a week. It looks very healthy. I am now going to harvest some of the leaves after reading your article

    • Hello Leigh,
      that’s great. The leaves add a bit of zing to salads. Hopefully the rhizome will be big enough at the end of next year to harvest. Interesting to find out how the real Wasabi tastes like.


  4. Hi Marianne,

    Thanks for an excellent piece of commentary on what is… and isnt Wasabi…

    I’ve been eating “isn’t wasabi” and want to try to grow some from seed… A lot of it actually. I have friend who moved From Sydney back to HK to start a Wasbi farm as a micro business. He sources his seed locally there and I am sure it wouldn’t get past AQIS.

    Do you know where I can source some certified organic (preferably) Wasbi seed from please? Diggers only seem to want to supply the plant. The other links site doesn’t seem to be working.

    Thanks again
    Kind Regards,
    David Trees

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