Eutrema japonicum

Wasabi is an herbaceous perennial, native to Japan and Korea, and is in the same family as cabbage, horseradish, and mustard. Naturally grown along rivers and streams in mountainous areas, it grows well in environments where you would typically find ferns.

The root is a horseradish substitute and the ground rhizome has the pungent spiciness of horseradish and, when finely grated and prepared into an attractive fresh green paste, is a popular condiment in Japan. All parts of the plant are edible, especially the rhizomes, which can take up to three years to mature to a harvest size of 1 inch in diameter.

Plants may be difficult to find in garden centers, and few places are suitable for large-scale wasabi cultivation, which is difficult even in ideal conditions, however, seeds are available online. The best time to plant seeds is late fall to early winter because they need approximately two months of cold temperature before they sprout. Alternatively, seeds can be kept in the refrigerator for two months, and planted outside when the temperature is around 50-55 degrees. Seeds should be soaked in distilled water overnight to soften the outer covering to accelerate germination.

Plant Wasabi in organic, loose, and crumbly soil with good drainage, but good moisture retention. Coarse sand can be added to improve drainage. The best temperature to grow Wasabi is between 46-70 degrees. Sow seeds in heavy shade or under a canopy of trees where it will be cool, moist, and humid. Plant two inches deep, with rows two inches wide, and plant one seed per hole. If planting in a container, thin and transplant to a larger container, at least 10 to 12 inches deep and wide and set the container in a shallow pan of water.  A small amount of slow release 12-12-12 fertilizer is adequate for 3-4 months. Keep plants well-watered, but not standing in water.

Harvest rhizomes by pulling the entire plant out of the ground. The best flavor is derived by grating the cleaned roots within thirty minutes of harvesting, but can be kept refrigerated for a month. Rhizomes can also be dried and ground for a longer shelf life. Wasabi can be propagated from plantlets that grow around the primary plant, or by dividing rhizomes. Wasabi is high in vitamin C, and also contains vitamin A and iron.

Insects, Diseases, and Other Plant Problems:  In some cases, it is susceptible to aphids, alfalfa looper larva, cranefly larva, slugs, leaf spot, root rot, or rhizome rot.  Prune wilted, damaged, or dead leaves to deter pests and diseases.