Garden Wasabi Planting: What To Do and What Not To Do

First I want to reiterate that our home garden wasabi planting is intended to approximate a laissez faire gardener environment, with no special treatment, hot and dry conditions in the summer and cold in the winter (relative to the Oregon Coast) to test the plants' response.  See this former blog post for more.  This was done to such an extent that we intentionally did' t follow our own recommended planting instructions.  Thus, I've structured this blog episode into "our preparation" and "recommended preparation" which is the information that accompanies plant start purchase packages.  I can assure you that we are not laissez faire at the Frog Eyes wasabi Farm - and not about much else if truth be told.  But, I want to assure the readers that there's no special treatment or hidden magic being applied to the plants in our home garden (this garden needs a name don't you think?).  This summer, 2016, I planted an additional wasabi plant start half-wine barrel with an intention to display the correct way to plant wasabi and the incorrect way and the results.  

Our Preparation: (Note, this is what I did, and not necessarily best practices.) Soil/media: First, I planted a half-wine barrel using store-bought organic potting oil and about 25% large, 1-inch pumice for drainage and oxygenation.  Sunlight: Unlike the initial barrel that receives sunlight in late January and early February in the early morning, I placed the barrel in a location that receives sun in months 3/4 and 8/9 at about noon for about 1.5 hours. This to increase the sunlight strength at a much stronger solar period.  I planted small plant starts without leaves and larger ones with leaves. This was done to display the plant's accommodation of inhospitable conditions at different growth stages. I also planted at the hottest week and driest week of the entire year, with temperatures at 100dF and humidity between 15-30%.  

Recommended Preparation: 

Planting Depth: 1 inch or less - Only deep enough to keep the start upright;  Spacing:   12 inches on center;     Hardiness: 27°F;     Soil Type: Well-drained, rich in organic matter    Location: Full Shade  

Choose a well-drained location with sufficient organic matter. If you’re planting in a pot the container size should be 10 inches or larger (a 2.5 gallon minimum). Work in 10-12 inches of compost to a soil depth of 8-10 inches. Wasabi requires a neutral or slightly acidic soil pH of 6-7.  Plant your start only deep enough to keep it upright.  Being sure that all of the roots are covered, backfill the hole and gently press into place. Do not cover the rhizome, it needs to be exposed above the surface. Wasabi plants can reach 24 inches in height so space plants at least 12 inches apart. Water well, but do not let the plant sit in drainage water. After initial planting irrigate regularly with cool water. Mist as necessary to keep plants cool and to avoid wilted leaves. Mulch may increase moisture retention, which will be especially beneficial during warmer months.   Leaves that have been wilted for a week or more should be removed to deter pests and lower the risk of disease. Keep the planting bed or containers weed free and fertilize regularly with a balanced, all-purpose fertilizer. Fertilizers or foliar sprays rich in sulfur may improve the flavor of the rhizome. 

Cultivation: In its natural habitat you will find Wasabi growing on the shaded wet banks of cold mountain streams. When grown in a home garden Wasabi does best in full shade with steady temperatures between 50-60°F, although the Daruma variety is slightly more tolerant of heat and light. Temperatures below 40°F may slow growth and temperatures below 27°F can kill the entire plant. Temperatures above 80°F can begin to cause heat damage as well as increase the risk of pests and disease. So take this into consideration when selecting a planting sight for your Wasabi.

As seen, there's loads of sunlight.  We do not recommend any direct sunlight at any time of the year.  Wasabi grows in alpine streams at elevation and under evergreen canopy.  If one should err on sunlight or shade, give wasabi shade.

Our Method: The larger plants were potted.  Continuing on the laissez faire gardener condition, they "rested" on the side of the currently-planted wasabi barrel for a few weeks, receiving no sun, and some water and routinely being kicked over by our faithful hound.  The first photo below shows the potted plants prior to planting and the volume of pumice used for the top layer of potting soil and the sunlight.

Recommended Method:

Showing the potted plant hole depth.  I add a bit of pumice at the bottom of the hole for root drainage.  

Photo taken several minutes later after the sun was shaded by the house.  This photo shows the backfill to the potted plant hole and the plant spacing which is about 8 inches on center.

This photo shows the new plant starts that are new.  This is how the first wine barrel's plants began.  This photo shows their size and the bare root condition.  This is how The Wasabi Store ships plant starts.  They are nearly always successful, unless planted on the hottest day and driest day(s) of the year and with direct sun.  The potted plants were once just like these about two months ago.  I recommend that if you order plant starts in the summer to plant them in a cloudy and cool week.  If they arrive during a hot spell, keep them in the refrigerator in a plastic bag and wrapped in a wet muslin or paper towel (just like the storage instructions for the mature rhizome).  They will be much happier in the cool, damp refrigerator.  These are not your typical plants.  Don't panic about "getting them in the ground as soon as possible" or other common plant-planting axioms.  I'd recommend the maximum time in the refrigerator is 3 weeks.  If it's going to be that hot during your summer, wait to plant in the autumn so the plants are established for the following summer. 

Having planted the small starts just like the others.  Soil almost, but not up to the bottom of the stems.   Don't worry about root oxygenation like other plants.  Don't pack the soil.  Just water and let the water weight pack the soil.  Oxygenation is encouraged, not discouraged.   See how the plants are planted with soil just to the bottom of the rhizome?  That's the correct depth.  More soil can always be added later.  It's better to not smother the plants and allow air in, rather than make too damp an environment.  


Showing one week later after the heat wave.  The small starts are dry.  The established plants have endured the incompatible conditions. 

Showing apical meristem growth in an established plant just days following the heat wave.  They actually grew during this time.  

Showing small leaves in the center, the apical meristem growth again.  This week is cool and rainy.  I'll have an update on the small plant starts in about 10 days.  Wish them luck on their recovery!

Pests and Diseases: Wasabi is a member of the Brassica family. Pests and diseases of this family include: aphids, cabbage and alfalfa looper larva, crane fly larva, and slugs. The best defense against pests and disease is to maintain the cool temperatures and stable irrigation wasabi prefers. Pruning wilted or diseased foliage, hand removal of slugs or use of slug bait, and removal of aphids and other pests is beneficial to the plants health. Use caution when using any insecticidal soap or any other insecticides. If any fungal disease is detected it is recommended to remove the plant away from all others to try treating it, or dispose of the plant entirely. Copper spray can be useful in the presence of any fungal complications. 

Harvesting: If conditions are optima, within 24-36 months from the initial planting, you may harvest a four inch or larger rhizome. In the meantime, you may harvest the petioles (leaf stems), leaves and flowers that bloom in the early spring. All parts of the plant are edible. However, overharvest of leaves can lead to slower rhizome growth.

The whole wasabi plant is edible.  Enjoy harvesting and eating the leaves and leaf stems raw or cooked while you wait for your rhizome to grow!  When your rhizome is ready to harvest it is recommended to hand dig the plant out of the ground or pot. You can then remove the plantlets that have formed around the crown to be potted or planted and expand your wasabi crop. Trim away the roots and stems and enjoy your fresh wasabi.

Update: Late September 2016.  The plant starts that had no leaves all died.  I've not seen such a rapid demise.  This was because I planted both on the hottest week of the year and with some direct sunlight.  The plants simply were brought beyond their tolerance at such a young age.  The other plants continued to grow and are thriving. Lesson: if it's too hot, keep the plant starts in the refrigerator or initiate them outside the garden and wait for a period of appropriate days. 

This photo was taken on the same day as the above.  This plant was started in the pot and, though planted at the same time (hottest day .....), it is continuing to grow.  

Posted on September 1, 2016 .