Growing wasabi plants at home is worth the challenge because you will be rewarded with a prized fresh rhizome. Wasabi is considered to be a difficult plant to cultivate and maintain. However, if you buy some wasabi plant starts from our shop you will be in a good situation. These hardy wasabi plants are ready to go for your garden or as a house plant. Yes, wasabi can be challenging to grow and is susceptible to its environment, temperature, humidity and water content. The rhizome can take up to 2 years to mature and while you wait, you can enjoy the wasabi leaves and stems.
Wasabi, known as Wasabia japonica, can be grown in a shade greenhouse or polytunnel. However, if you do have any of these facilities, you can grow wasabi in a shady part of your garden. Wasabi plants require sulfur enriched fertilizer, good soil, compost gravel of pea-shingle and at least 70% shade cloth.
Wasabi plants tend to grow best in a temperature range of 7°C to 24°C. However, we have been growing wasabi plants in a shaded polytunnel in the past four years and the plants have experienced all four seasons. Yes, the summer season can be challenging and the temperature in the polytunnel can reach 40C. In this situation, to destress the plants, we give them an occasional sprinkle of water from the overhead water system and found that this works quite well in conjunction with the shading cloth.
The natural habit of wasabi plants can be found alongside the mountain streams of Japan. The ‘wild wasabi plants take the shade from the umbrella of the tree branches. So, plant your wasabi in a well-shaded place and keep them out of direct sunlight. If you do not have any big trees in your garden, you can always use the shade cloth.
You may want to grow the wasabi plant in a pot or a container such as an old wheelbarrow. In all cases, make sure that you put some drainage holes, so the plants do not sit in puddles of water. A typical pot says 10 litres with several drainage holes fill the bottom with a layer of pea-shingle about 5 cm in depth. Then fill the pot with a mixture of soil, compost and fine gravel. In the centre of the filled pot, dig a hole and carefully place the wasabi plant start and give it a good watering. After, place the pot in a shady part of the garden. The advantage of using containers to grow wasabi is that you can move them around the garden or take them into the house.
However, you may want to plant your wasabi starts directly into the garden soil. The best approach is to find a patch of soil in a shady part of the garden and, if required, roto-tiller the soil or dig down to at least a foot and turn over the soil. At this stage, you may add some sand or gravel to provide good drainage. To test the soil drainage, take a handful and clinch to see if it does not clump together. Also, it is essential to test the pH of the soil and aim for between 6 and 7. This pH range seems to be the best to grow wasabi plants. Then apply some fertilizer (NPK 12:12:12) and compost into the soil and work in and make sure you maintain good drainage. You can check this by soaking the soil and see it drain away. If the water drains very slowly and forms puddles, add some compost to the soil and mix well. At this stage, you should be ready to plant your wasabi starts.
My advice is not to start from seed. This is because if you buy wasabi seeds from the internet, you will likely receive mustard seeds. The only way you will obtain real wasabi seed is to visit a wasabi farm in Japan and even if you went to this extreme, to may not get your hands on wasabi seed.
Plant your wasabi starts in rows at least 12 inches apart to allow the plant to develop. Wasabi plants tend to spread out, so more room is better. It also allows you access to harvest the leaves and stems when required, especially for your salad or sandwich.
Once you have finished planting all the wasabi, please give them a good watering and, most crucial, periodically look at how the plants are doing throughout the year. If the plants begin to wilt, that’s a sign they are not getting ample water. Also, remember not to give too much water as this will encourage root rot. Since the wasabi plants are growing in fertile soil, this will encourage weeds and therefore, it is important to remove them, so regularly check your plants. Finally, after two years of waiting for the prized wasabi rhizome, sometimes known as wasabi root, you can harvest. However, you can enjoy the herbal green heart-shaped leaves and stems to add the zingy wasabi flavour to your salad and sandwiches during the two years of waiting. At the harvest stage, the wasabi plant will be about two feet tall and two feet and the rhizomes will be 7 or 8 inches long.
Wasabi harvest day
After waiting two years, you can start to dig up the rhizomes. If you have several plants in the patch of soil, you may want to check for a rhizome. To do this, place your hand in the near centre of the plant and find the crown, which is the head of the rhizome. When extracting the rhizome, carefully dig around the plant to loosen the soil and pull on the plant, but be careful not to damage the rhizome and if you are lucky, it might beat the British record, which stands at 355 g. Also, you can have more than one rhizome off one plant.
The rhizome will have offshoots on it and you can carefully remove these and these plantlets can be used to grow more wasabi. The fresh wasabi rhizome then can be store in the fridge for up to 28 days and enjoyed with your favourite dish. Also, real fresh wasabi is full of nutrients, vitamins, antioxidants and minerals.
I’m Sofia Kitson, the Wasabi Crop Blogger. My interests are writing articles on growing and cooking with wasabi.