What is Wasabi?

Wasabi or Wasabia japonica is a Japanese plant belonging to the brassica family and is sometimes referred to as Japanese horseradish. The heat and flavour that’s generally associated with wasabi comes from wasabi stalk or rhizome which is grated with a special wasabi grater. It is most commonly eaten as an accompaniment to raw fish such as sushi or sashimi although it is very versatile and apparently has a multitude of ways in which it can be used.

Can wasabi be grown in the UK?

Whilst it may not be possible to achieve exactly the same results as natively grown wasabi, it is possible to grow it in the UK. Furthermore, the cloudier and cooler the British summer, the more wasabi plants flourish. Although it is tricky to grow many gardeners claim the effort is worth it, and they enjoy the challenge.

Can I grow a wasabi plant from seed?

Wasabi can be grown from seed but they are incredibly difficult to germinate. They’re also difficult hard to source, even from commercial suppliers because they are difficult to harvest. For that reason, we advise getting a wasabi plug plant or young plant and growing that instead.

How long does it take for wasabi to grow?

Now patience really is a virtue, especially when it comes to growing wasabi specifically to harvest it for the rhizome. Wasabi plants produce large heart or kidney shaped leaves as it slowly grows. It can take two to three years for the plant to produce the precious rhizome at which point it will be around 2 foot high and wide. Whilst you’re waiting for the rhizome to appear you can pick leaves and stems throughout the spring through to summer and eat those. In fact, everything on a wasabi plant is edible including the white flowers.

Where to plant wasabi

Wasabi plants require very specific growing conditions. It is accustomed to growing near streams in Japan under large overhanging trees which provide a lot of shade. Therefore, it has evolved to survive in very low light levels and direct sunlight will not be tolerated, it needs to be planted in the shade, under a tree, large bush, against a wall or fence.

When to Plant Wasabi

The ideal time to plant wasabi in the UK is during the cooler months of autumn or early spring. Aim to plant between September and April to take advantage of milder temperatures and ample moisture, which promote strong root development.

How do you prepare soil for a wasabi plant?

Sourcing a wasabi plant from a local nursery is usually quite tricky so it’s often easier to order them online. When you have your wasabi plant it is recommended that you re-pot it into a 9cm pot to develop a strong root structure prior to planting out.

Wasabi plants in the garden require rich, consistently moist soil with a pH of 6-7. Use a slow release fertiliser which is sulphur rich as this helps the flavour to develop.

How to Plant Wasabi

When planting prepare the soil bed with a gentle slope by digging a hole and mix in loose, rich, organic compost with fertiliser and fine sand. Soil needs to retain moisture as well as be free draining as wasabi is prone to root rot. In order to ensure good drainage, cover the entire area, which the plant will consume, with three to four inches of pea shingle. Place the plant in the shingle so the crown is not covered, but remains slightly above the soil so leaving part of the rhizome exposed and any new leaves can grow undamaged.

The pea shingle will allow roots to grow down into the compost and the rhizome will grow through the shingle. It will also help retain moisture, keep roots cool and suppress weeds.

Can you grow wasabi in containers?

Growing wasabi in containers is possible and a good way to ensure that you can move it around and keep it in the shade. It’s advisable that the minimum size of a container should be a least 9 litres. As with planting a wasabi plant directly in your garden, the soil needs to be well prepared with good drainage.

How and when to water wasabi plants?

Wasabi plants are ultra-fussy when it comes to being watered; too much - they rot and die and too little - they die. They don’t like wallowing about in water either. However, they do like their leaves to be misted regularly and some serious growers suggest setting up a micro irrigation system.

What does the temperature need to be for wasabi to thrive? 

Wasabi tolerates a temperature range between 7 and 24 degrees and respond negatively to sudden and large temperature fluctuations. This is why it needs to be planted in the shade or  containers, which means it can be moved into the shade. During the colder months the plants will need to be protected which fleece blanket and some straw or to cover the crown of the plant.

What pests and disease are wasabi prone to?

Wasabi is in the Brassica family and so any bugs that love to eat cabbage or broccoli, such as cabbage worms will also enjoy munching on wasabi, micromesh protection barrier is a good insurance against this.

Be prepared for slugs to start munching their way through the leaves too which, a well-established and mature plant can survive but young plants need protecting form. Pick slugs off by hand or creating a slug free zone around the base of the plants with beer traps, sharp mulch or organic pellets. Insecticidal soaps are not recommended for wasabi.

If affected by a fungal disease make a baking soda spray by dissolving one teaspoon of baking soda into one quart of water to spray on your wasabi plants.

During the colder months remove dead leaves as they die back whilst the plant's energy travels down into the rhizomes that will be developing at the base of the stems.

How do you harvest wasabi?

It can take between two to three years for your wasabi rhizome to fully mature and develop before it can be harvested. Dig up one rhizome, if it is 7 inches or more long then it is ready and you can continue to harvest the rest of the crop, but be careful not to cut or damage it.

To consume wasabi, shave off as much as you need or grind into a paste. Don’t go mad though and only grate what you need as the heat of the wasabi fades after about thirty minutes

Can you store fresh wasabi?

Fresh wasabi can be stored in the fridge for a month or so before it will perish. To store it for longer periods of time dry out the wasabi, grind and store in a powder form.

Let us know how you get on with growing your own wasabi and tag us in on your social media posts.

Did you know Wasabi is the most expensive crop in the world?

But why is real wasabi so expensive?

Wasabi rhizome is like green gold because it is the most difficult crop to commercially grow. Wasabi plants require super specific growing conditions and naturally thrive by shady rivers and stream beds high in the Japanese mountains. In addition to fussy requirements, they can take up to three years to reach maturity: to grow any crop commercially with such a long growing season means it is highly susceptible to problems, pests and diseases.