How To Plant, Grow, and Care for Wasabi

Wasabi is king for sashimi or sushi, but 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 perennial. 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 with nutrients, it’s difficult but doable if you know how to grow it. A member of the brassica family, this Eutrema japonicum, syn. 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-drained environment this aquatic first evolved in.

Shade is absolutely required, as is slightly sulfurous soil and very consistent watering and weeding. Wasabi can grow from rhizomes and can take a few years to grow. While difficult to self-seed, most people find plantlets to get their harvest going. 

Many areas of the Pacific Northwest and British Columbia successfully keep farms 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!

What is Wasabi?

Wasabi, or Eutrema japonicum, grows from an underground rhizome along stream beds in shady areas and cool temperatures of mountainous Japan. A slow-growing perennial, it can take several years to mature. The roots are the coveted portion, even though the entire perennial is consumed. 

This root of wasabi is ground up into a wasabi paste and served with many different fish or vegetarian sushi. 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. 

Native Area

Originally from Japan, wasabi is now known worldwide for its sushi-popping qualities. Its range covers the Korea peninsula and the northeast Asian island of Sakhalin. It was also introduced in Taiwan.

Characteristics

Slightly strange-looking, 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 one to two inches and reach a depth of up to 18″.

They sprout several long leaf stems that can reach up to 12″ in height. Large heart-shaped and bright green leaves perkily rest on their stems and soak up what little light they need. While it doesn’t always flower, it 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 two to six seeds per pod. 

Due to the part of this world that these 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. 

The health benefits of the actual plant, when grown at home from wasabi seeds or rhizomes, are undeniable. While initially only eaten with raw fish, it is also eaten for its leaves, which can be pickled with sugar and salt to make a dish called zuke. Alternatively, the leaves can be eaten cooked or in salads.

Planting

If you’re growing wasabi from plantlets, i.e. smaller growths on a rhizome of a larger wasabi, it’s best to start them in the fall. Wasabi grows the most during the cool season, between fall and spring when they are most likely to receive steady water (either rainwater or distilled water).

Place your plantlets in well-drained soil, gravel, or a rooting medium similar to vermiculite in late fall. While commonly grown in the United States in the Pacific Northwest along the Oregon coast, this semi-aquatic can also be grown in aquaculture in a raised planting bed with organic soil and a very well-drained planting medium.

Running water is ideal. If denied these conditions, wasabi falls prey to mainly fungal disease, as the wet soil incubates various diseases. 

To grow, 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 two inches of sand over three inches of gravel, with 16-40″ of small rocks as the bottom layer.

Within the bed, there is a slope of one to four percent, which encourages an ever-flowing stream of water.  Plantlets should be transplanted when they’re about one and a half inches tall and have sprouted four to five true leaves. 

You can also grow wasabi in containers where the conditions can be easily controlled. Use shade cloth to keep new wasabi from direct sunlight, or place them in a greenhouse in full shade. 

If you’re growing wasabi in the ground, transplant plantlets at a minimum depth of two inches for their long roots in containers with greater depth than usual. The root needs more space than most in order to grow. 

How to Grow

Growing wasabi can be quite difficult, as it is known to be one of the most difficult 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 replicate those conditions best. 

Light

Wasabi thrives in mild temperatures. Its leaves need a shady location with no direct sunlight. Try replicating these conditions by providing shade in the form of shade cloth or a large tree. Add compost to your planting medium to a depth of ten inches to both provide nutrients and insulate the roots from extreme temperature fluctuations. 

Water

Wasabi needs water continuously delivered to its root zone. It’s the ideal perennial to grow in a water garden or in containers where the soil can be kept continuously wet – wetter than many other types 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%. 

Soil

Wasabi isn’t grown in conventional potting soil. For growing it, you’ll need to locate a very well-draining growing medium such as vermiculite, sand, and gravel, or even try going the aquaponics route. A soil pH of 6.0 to 7.0 is best.

You can try growing in the Tatamishi system described above, 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 type, it might be best to try a few growing methods at once and see which works best for your growing environment. 

Temperature

The temperature range should be between 46-70°F (8-21°C). Above 80°F (27°C), wasabi can die, while under 27°F (-3°C) they can freeze. 

Fertilizing

Your 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 at the time of transplanting. Additionally, apply a foliar spray to the leaves about one to three months before harvest to improve flavor. 

Propagation

Widely considered a very difficult one to grow, the wasabi root is more often propagated through vegetative propagation – the plucking of smaller plantlets off the crown of the mother and placing them in ideal, moist, and shady conditions to create a whole new set of wasabi. This is considered the fastest way to grow large quantities. 

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 when several months of ideal growing conditions are on the horizon. 

While difficult to grow from seed, it is possible. Known for their low germination rates, if you do get some of the wasabi seeds or seed shells, try over-planting and expect under-germination. Additionally, suppose they haven’t already been stratified. In that case, you’ll need to put the wasabi seeds in the fridge for two months to simulate a cold period for the wasabi seeds to go dormant. You can expect a germination time of three to four weeks. 

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 if you can’t find the more traditional starts. 

Harvesting

The easiest part of growing is enjoying the fruits of your labor! Wasabi is edible at almost every stage of its life. However, it is usually harvested when the stalks are about four to five inches above the ground and one and a half inches thick. 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. 

Storage

Wasabi is 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 it to lose some of its precious nutrients. There are no unused portions of wasabi, as the entire perennial is edible. Try adding its leaves and stems to a salad or pickling them to make wasabi zuki. 

Common Problems

Wasabi is difficult to grow, and you may encounter a few problems in a couple of years when you are growing it. One of the most common problems with growing wasabi is finding rot. To fight this problem, try searching for rot-resistant starters. Several varieties 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. 

Pests

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.

Several caterpillars feed on the leaves of wasabi. Handpick these off the leaves, and use Bt to treat them if necessary. Stop using Bt a couple of weeks before harvesting.

Diseases

Wasabi suffers from a plethora of fungal diseases including leaf spot, root rot, rhizome rot, and 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 survive the disease, especially given how long it is to harvest. Remove severely damaged ones. For some wasabi, simply removing damaged leaves is enough. You can remove as much as needed and see if it recovers.

Frequently Asked Questions