Wasabi has a reputation for being a gardening challenge because it has very specific growing requirements and takes years to mature. Don’t let that deter you. With some TLC, you can make it happen.
Often, people think they have tried wasabi in their sushi box, but that hot green past is likely a mix of horseradish, mustard, and green food coloring. Real, fresh wasabi is smoother to the palate.
In the wild, this wonderfully fragrant Japanese plant often grows along rocky river beds and riverbanks where it gets plenty of water and shade. Those are the conditions you’re going to need to recreate.
Varieties of Wasabi
There are dozens of varieties of Wasabia japonica. Here are some of the standouts. The stems, often called roots or rhizomes, grow to be about 6-12 inches long and 2-4 inches wide.
Most wasabi plants have a spreading growth habit, but a few grow upright instead.
Wasabi is a member of the Brassicaceae family, along with plants like broccoli, cabbage, and of course, mustard.
This is one of the longer growing wasabi plants. It can take up to 36 months for the stem to be ready for harvesting. Mazuma blooms with delicate, edible white flowers in the spring. It has a spreading growth pattern.
Daruma has lovely, thick leaves you can eat while you wait for the root to mature. The thick stems are upright and topped with heart-shaped leaves. It has a particularly excellent flavor.
This is one of the most popular varieties to grow because it can stand higher temperatures than other wasabi. It’s also resistant to black leg and soft rot. This is a partially upright, partially spreading variety.
If you’re looking for a quick grower, check out this variety. It’s ready to harvest with a high-quality stem in under a year. Fuji Daruma has a spreading growth habit.
Green Thumb is a modern variety popular in commercial wasabi operations. It’s a particularly good variety if you want to eat the leaves.
Midori is a good variety if you’re growing wasabi in smaller amounts because when grown in large numbers, it’s particularly susceptible to fungal diseases. It’s a quick grower with bright green leaves and has an upright growth habit.
Sanpoo is a variety developed for poor quality soils. If you don’t have rich earth in your garden, this may be a good option, though the stem isn’t as flavorful as some other types. It’s resistant to soft rot.
Shimane has delicate, spindle-shaped roots, with tasty stems, leaves, and flowers. It has an excellent flavor, though it’s susceptible to disease. This plant has a spreading growth habit.
Medeka is another variety that grows well in less than optimal conditions.
This type has thin, high-quality stems and the plant is high-yielding. The stem is light purple, so it adds a pretty look to your dinner plate.
This variety is bolder in flavor than some other types. It has a strong spicy, sweet taste in both the abundant leaves and the stem. It grows in a spreading habit
How to Plant Wasabi
BBC called wasabi the “hardest plant to grow” for a reason. Commercially, it’s extraordinarily hard to grow, which drives up the value. At home, it’s a little easier to figure out, but make no mistake, it’s a challenge.
Although wasabi grows in streams in the wild and in commercial operations, I find that to be impractical for the home gardener like me. I grow it in soil or containers, and you can grow wasabi indoors or out.
In the U.S., wasabi doesn’t grow well outdoors in most regions, but it does well in temperate areas like the Pacific Northwest.
That said, wasabi will grow anywhere in small quantities if you’re willing to do some extra work to keep it happy. You have to be mindful of temperature rather than zones. Wasabi likes to be not too hot and not too cold.
If the temperature exceeds 80°F or goes below 32°F, you’ll need to take action. You can do things like adding shade cloth or moving the wasabi indoors.
If you regularly get outside of these temperatures throughout the year, you’ll probably need to grow indoors.
Here’s where a lot of people go wrong. Wasabi doesn’t need partial shade, it needs full, heavy shade.
If you plant wasabi in the garden, make sure to put it in the right spot. If you plant wasabi in pots, you can move them around if there’s too much sunlight.
Wasabi will wither if its gets consistent sunlight.
Wasabi does best when it’s growing in shallow, cold, clear running water. Not everyone has a shady, cool, stream running in their yard, however. Instead, you can grow wasabi in soil without the moving water, provided that you keep it moist.
If you plant wasabi in the garden, aim for well-draining soil that you can keep consistently damp. A pH of 6 to 7 is best.
You can also plant wasabi in a hydroponic set-up.
I much prefer planting wasabi in containers over planting in the garden. You can move the container inside if it gets too hot or cold.
If you keep your containers indoors, a basement with good airflow, but out of the sunlight is sufficient.
Use a large container with a good, rich, moisture-conserving potting mix.
Wasabi can be propoagated by seed, transplants, or cuttings.
Wasabi seeds can be hard to get hold of and, unfortunately, many seeds for sale out there aren’t true wasabi. They’re actually mustard, wasabi mustard, or arugula wasabi.
If you are lucky enough to get seeds, soak them overnight in water and plant them in seed raising mix in the morning. Keep the mix moist until they germinate.
Plant seeds in late winter or early spring when temps are in the 50s to give them time to strengthen.
Start them indoors in containers in the middle of winter. Once the wasabi is at least six inches tall, you can plant in the garden or bigger containers.
I’d suggest starting a bunch more seeds than you expect to need because you’re likely to have some failures along the way.
There are a few retailers who sell wasabi starts online. I suggest you buy some starts if you’re able. They are far more reliable and you know it’s true wasabi.
If you can get your hands on transplants, you’ll need to transition them for about a month before you put them in their permanent spot, whether that’s a container or a place in the garden.
Wasabi plants send out little offshoots that you can snip off at the base and plant in a 50:50 mix of sand and compost. After two months, they should develop roots and you can then transition them to their permanent home.
Planting Wasabi in the Garden
When it comes time to transplant, choose a shaded spot under a tree or structure that provides plenty of shade. Use a shade cloth or tarp if necessary.
I can’t emphasize enough that wasabi is a shade lover, but if you live somewhere that is overcast much of the time, such as the coast of Oregon or Washington, you may be able to plant in dappled shade under Adler, evergreen, or poplar trees.
Ideally, you want a humid, temperate environment.
Over the next four weeks, gradually introduce your starts to the new spot they’ll be living in. Start with an hour the first day and add an hour every few days until it is able to stay outside full time.
Then, dig your soil to a depth of about 10 inches then dig in good quality compost. The soil should not be compact. Although the greens of wasabi are edible, it’s the stem we’re after and we want the soil to allow a deep growth.
Then, water the plant well and keep moist.
Plant your wasabi six inches apart with rows six inches apart.
Caring for Wasabi
The hardest part’s over, but the job isn’t done, yet. Now it’s time to care for those wasabi plants.
The wasabi plants can be in the soil for two years before you’ll harvest it, so it will need additional feeding. It’s also a hungry plant that needs lots of nutrients.
Feed with good quality fertilizer, remembering not to deviate from a pH pf 6.0-7.0. A 12-12-12 fertilizer works well, as does poultry or green manure.
If your wasabi is in a container, use a well-balanced fertilizer specific to plants in pots.
We know by now that wasabi loves shade, but it also needs a lot of water. It naturally grows in little streams of moving water. If you’re growing in soil, don’t allow the soil or potting mix to dry out. It should be consistently moist at all times.
Keep the area around wasabi completely weed-free. Wasabi does not like to share its space with weeds. Be especially careful to pull any wild mustard or bittercress, because these plants are also in the Brassicaceae order and share diseases with one another.
Companion Planting for Wasabi
Wasabi plants should grow too close next to other plants. It’s not really the companionable type. However, about a dozen feet or so away, you could plant things like:
Common Problems and Solutions for Growing Wasabi
Unfortunately, wasabi falls prey to quite a few pests and diseases. It’s in the mustard family, after all.
Watch your wasabi greens especially when they are young. Use slug pellets or whatever method you prefer to rid your garden of slugs.
These little sap-sucking insects attack pretty much everything and wasabi is no different. Given wasabi is in the soil for up to two years, I like to use natural techniques so chemicals don’t build up in the plant.
First, spray plants with a blast of water to knock aphids away. They may just leave anf find a better host. You can also dust plants with flour. It sounds weird, but it constipates the little suckers and kills them.
If that fails, apply neem oil three times a week for two weeks. If that doesn’t work, try organic pyrethrum with the neem to really knock them out.
Crane Fly Larvae
These pests live in the soil and attack the plant from underneath. They will come out of the soil at night and feed on dead foliage.
Use an organic insecticide or apply regular applications of neem oil to control them.
Wasabi is susceptible to rotting roots because of the consistently wet soil.
This fungus can be incredibly destructive when it comes to growing wasabi. It first shows up as black spots on the leaves and stems of the plant. These circular spots eventually become holes.
The root will rot and eventually die off. Once you’ve got it, there is no cure. Pull the plants and don’t put any brassicas there for at least three years.
In the future, purchase certified disease-free seeds and look for resistant varieties.
Internal Black Rot
Internal black rot is caused by bacteria and fungus that team up to turn the veins of growing wasabi plants dark. After that, dark spots appear, which turn milky and smell awful.
Plant leaves may or may not turn yellow and the root may rot or turn yellow as well. While there is no cure, your plants may recover if you can provide them ample moisture and shade.
The disease thrives when the weather heats up, so you need to protect your plants. In the future, purchase resistant varieties.
Yellow and Wilted Leaves
This can be many things, but with wasabi, it’s often too much sun. It seems strange to say a plant can have too much sun, but wasabi much prefers shade. Consider using shade cloth or of the wasabi is in a container, move it to a shaded area
If your wasabi is yellowing and stunted, but the shade is fine, consider a side dressing of fertilizer. This is especially important when the wasabi has been in the soil over a year.
Wasabi is a plant that requires patience. If you dig into the soil to harvest the rhizome before it’s ready, you’ll be disappointed. It really does take up to two years depending on the variety.
Don’t despair though. All parts of the wasabi are edible so after eight months or so, you can start enjoying the leaves, stems, and flowers that bloom in spring. Just remember, the more of the leaves and stems you eat, the slower the stem underground will grow.
Use the leaves fresh in salad, pickled, sautéed or in stews. They contain heat and the stems are hotter than the leaves.
After two years – or sooner, if you have a quick maturing type – dig down carefully to reveal your lovely wasabi root. If you plan to sell your plants at the market, be sure to leave some of the leaves attached. This helps buyers know that they’re getting fresh wasabi.
Clean it with water and cut off any lumpy bits. Use the finest grater you can and grate to a fine paste. Use only the amount you need as wasabi loses that wonderful pungent flavor in about 20 minutes.
Store the remaining root in a damp paper towel and place in the fridge. You must allow them to breathe. Don’t wrap them in plastic.
Use the paste on sushi, sashimi, oysters, steak and anything else you fancy. You’ve waited a long time for this, so enjoy it!