For sashimi or sushi, wasabi is king — and yet very little of what people purchase as “wasabi” in the United States is actually real wasabi, as real wasabi is known to be a very tricky plant. Usually, the bright wasabi paste found in those tubes is actually European horseradish with food coloring! But for lovers of Japanese food, growing the real thing is worth it. Freshly grated and packed full of nutrients, it’s difficult, but doable if you know how to grow wasabi.
A member of the brassica family, this Wasabia japonica is a cool-weather-loving grower. Native to areas alongside streams in mountainous Japan, you’ll need to simulate the rocky, moist, and well-draining environment this plant first evolved in. Shade is absolutely required, as is slightly-sulfurous soil and very consistent watering and weeding. Grown from rhizomes, wasabi can take a few years to grow. While difficult to self-seed, most people end up finding plantlets to get their harvest going.
Many areas of the Pacific Northwest and British Columbia successfully keep farms of this plant where islands of leaves and roots live in mounded gravel beds as water trickles steadily by. There are in fact 18 varieties of wasabi, although in the US you’re most likely to only find the mazuma or daruma varieties.
People successfully grow wasabi, either in greenhouses or in very shady areas of their yard, year after year. While it takes about two years for your plants to come to fruition, growing this green-tinted rhizome is entirely doable at home, and in the meantime, you can harvest tasty leaves to use too!
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Quick Care Guide
|Wasabi, yama, ooi, Japanese horseradish
|Eutrema japonicum, syn. Wasabia japonica
|Days to Harvest
|No direct sunlight, filtered light only
|3-4” per week
|Humus rich, well-draining soil or gravel with soil pH 6.0-7.0
|Well balanced 12-12-12
|Leaf spot, root rot, rhizome rot & petiole blight
All About Wasabi
Originally from Japan, wasabi is now known worldwide for its sushi popping qualities. This root is ground up into a paste and served with many different fish or vegetarian sushis. While this root was originally used for its antibacterial properties to be eaten with fish, it is now used more so as a condiment than as a food-safe sanitizer.
The wasabi plant, or Eutrema japonicum, grows from an underground rhizome along stream beds in shady areas and cool temperatures of mountainous Japan. A slow-growing plant, the entire plant can take several years to grow to maturity. The wasabi roots are the coveted portion of the plant, even though the entire plant is consumed.
The health benefits of the actual plant, when grown at home from seeds or from rhizomes, are undeniable. While initially only eaten with raw fish, this plant is also eaten for its leaves which can be pickled with sugar and salt to make a dish called Azuke. Alternatively, the leaves can be eaten cooked or in salads.
Slightly strange-looking plants, fresh wasabi is grown in aquaponics, soil that doesn’t retain water or even gravel. The wasabi rhizome grows underground and can look much like a swollen taproot that protrudes above the ground when fully formed and ready to harvest. Rhizomes range in width from 1-2” and reach a depth of up to 18”. They sprout several long leaf stems that can reach up to 24” in height. Large heart-shaped and bright green leaves perkily rest on its stems and soak up what little light this plant needs. While it doesn’t always flower, the plants can flower in early spring and produce more seeds that can then be used for propagation. While it takes up to 60 days for the seed pods to mature, they form along long skinny stems and can look like tiny pea pods. There are about 2-6 seeds per pod.
Due to the part of this world that these plants evolved in, if growing wasabi from seed, you’ll need to stratify the seed. Provide a false winter by putting it in the fridge for up to two months. This process helps the seed to know when it’s time to leave dormancy and sprout.
If growing wasabi from plantlets, i.e. smaller growths on a rhizome of a larger wasabi plant, it’s best to start your plants in the fall. Wasabi grows the most during the cool season, namely between fall and spring when temperatures are cool, and plants are most likely to receive steady water (either rainwater or distilled water).
In late fall, place your plantlets in well-draining soil, gravel, or a rooting medium similar to vermiculite. Widely considered a very difficult plant to grow, the wasabi root is more often propagated through vegetative propagation – the plucking of smaller plantlets off the crown of the mother plant and placed in ideal, moist, and shady conditions to create a whole new set of wasabi plants. This is considered the fastest way to grow large quantities.
While commonly grown in the United States in the Pacific Northwest along the Oregon coast, this semi-aquatic plant can be grown both in aquaculture, or in a raised planting bed with organic soil, and a very well-draining planting medium. Wasabi need an environment that somewhat mimics the growing medium where they evolved along river beds. So running water is ideal, hence the popularity of aquaponics. If denied these conditions, wasabi falls prey to mainly fungal disease as the wet soil incubates a variety of diseases.
To plant, try using the tatamishi system, a Japanese rock mat system that provides moving cool water where the soil drains rapidly. Beds can vary in width and length, but consist of a layer of 2” of sand, over 3” of gravel, with 16-40” of small rocks as the very bottom layer. Within the bed, there is a slope of 1-4 percent which encourages an ever-flowing stream of water. It’s best to transplant plantlets when they’re about 1.5” tall and have sprouted 4-5 true leaves.
Many growers also plant wasabi in containers. Wasabi growing can be more easily controlled in this type of environment as a smaller amount of gravel, sand, or draining medium is needed in order to control the growing environment. Growers will also use shade cloth to keep their new plants out of direct sunlight or place them in a greenhouse in full shade.
If growing in the ground, transplant plantlets at a minimum depth of 2” for their long roots in containers with greater depth than usual. The root needs more space than most in order to grow.
Growing wasabi can be quite difficult as they are known to be one of the most difficult plants to raise. However, one rhizome can yield a much larger harvest given enough time and careful cultivation. This edible rhizome is very particular about its care and needs a gardener who will try to best replicate those conditions.
Sun and Temperature
Wasabi thrives in mild temperatures. Wasabi leaves need a shady location with no direct sunlight whatsoever and a temperature range between 46-70 degrees Fahrenheit. Above 80 degrees the wasabi plants can die, while under 27 degrees the wasabi plants can freeze.
Try replicating these conditions by providing shade in the form of shade cloth or large tree shade. Add compost to your planting medium to the depth of ten inches to both provide nutrients and insulate the roots from extreme temperature fluctuations.
Water and Humidity
Wasabia japonica needs water continuously delivered to its root zone. It’s the ideal plant to grow in a water garden or in containers where the soil can be kept continuously wet – wetter than many other plants can tolerate. Many growers outside the pacific northwest grow these in containers for this exact reason, as their temperamental nature needs specialized attention for the duration of their lives.
Wasabi is not at all drought tolerant. You’ll need to supply a continuous source of moisture if you plan on harvesting wasabi. Given the growing conditions it evolved in, it’s best to try and mimic a humidity level of between 90-95%.
Wasabi isn’t grown in conventional potting soil. For this growing endeavor, you’ll need to locate a very well-draining growing medium such as vermiculite, sand, and gravel or even try going the aquaponics route.
You can try growing in the tatamishi system described above, or directly into gravel along a stream, or in a 50/50 mix of sand and gravel in growing containers. Given the difficulty of growing this particular plant, it might be best to try a few growing methods at once and see which works best for your growing environment.
Wasabi doesn’t need much fertilizer. They’re slow-growing and as a result, can’t take too much fertilizer. However, it’s best to give them a balanced fertilizer (meaning the NPK numbers are all the same) like a 12-12-12 at the time of transplanting. Additionally, many farmers apply a foliar spray to the leaves about 1-3 months before harvest to improve flavor.
While difficult to grow from seed, it is possible. Known for their low germination rates, if you do get some of the seeds or seed shells, try overplanting and expect under germination. Additionally, if they haven’t already been stratified, you’ll need to put the wasabi seeds in the fridge for 2 months to simulate a cold period for the wasabi seeds to go dormant. You can expect a germination time of 3-4 weeks.
More likely, you’ll be able to source or find pups, plantlets, or starts (all the same thing). These are the baby plantlets that grow along the stem or crown of a more mature wasabi plant. With these starts, you can place them directly into your growing medium, ensuring that the root has sufficient room to grow downwards. This is best done in the fall with several months of ideal growing conditions on the horizon.
Also grown through tissue culture, this option is open to many large-scale farmers who want to grow sterilized products at a faster rate without spreading some of the many diseases common in this crop. This is a relatively new way to propagate plants and not something replicable outside a laboratory. In your search for wasabi, try searching for wasabi tissue culture plants if you can’t find the more traditional starts.
Harvesting and Storing
The easiest part of growing is getting to enjoy the fruits of your labor!
Harvesting & Storing
Wasabi is actually edible at almost every stage of its life. However, it is usually harvested when the stalks are protruding above the ground by about 4-5 inches and are about 1 1/2” thick. Simply pull the stalk gently out of the ground, trying not to break it in two. Remove the leaves and any rot at the base of the root.
It’s best used fresh and eaten raw after being grated. It usually only lasts about two months fresh in the fridge. It can alternatively be dried and powdered, but this causes the plant to lose some of its precious nutrients. There are no unused portions of wasabi, as the entire plant is edible. Try adding its leaves and stems to a salad, or pickling them to make azuke.
A difficult plant to grow, you may come up against a few problems in the 2+ years you are growing wasabi.
One of the most common problems with growing wasabi is finding root rot. In order to fight this problem, try searching for rot-resistant starters. There are several varieties that have been bred to be resistant to rots. Improve drainage in your growing area and remove wilted leaves that can harbor disease once dead and decaying.
Wasabi doesn’t suffer from too many pest problems. They’re much more susceptible to fungal problems. However, aphids are big fans of the wasabi leaf. Neem oil or insecticidal soap will handle the aphids easily.
Wasabi suffers from a plethora of fungal diseases including leaf spot, root rot, rhizome rot & petiole blight. It may be hard to differentiate between the diseases as many of them manifest with the same symptoms of wilted leaves, browning and blackening stalks and roots, and a greyish tinge to their leaves. Prevention is the best path to take as few plants survive the disease, especially given how long it is to harvest. Use a copper spray as a preventative for leaf spots.
Frequently Asked Questions
Q: How long does it take to grow wasabi?
A: 1-3 years on average.
Q: Is it hard to grow wasabi?
A: Yes. But it’s rewarding when you achieve harvest!
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Published at Tue, 14 Dec 2021 23:18:24 -0500