Eutrema japonicum (Wasabi): complete guide

Overview

Eutrema japonicum, better known as wasabi or Japanese horseradish, is a remarkable plant species native to Japan, Korea and Sakhalin. This plant is primarily cultivated for its pungent rhizome, which serves as a gourmet ingredient in Japanese and other Asian cuisines. It is a fascinating choice for gardeners wishing to diversify their growing and try something truly unique. Genuine wasabi is far rarer and more expensive than the surrogates commonly used in Western restaurants.

Appearance and bloom

Eutrema japonicum is a compact, herbaceous plant typically reaching 30-50 centimetres in height. The plant displays green, heart-shaped to kidney-shaped leaves with wrinkled surfaces. Leaves are approximately 10-15 centimetres long and grow on long petioles. The plant produces small, white flowers in spring, appearing in small clusters. After pollination, long, slender seed pods (siliques) characteristic of the Brassicaceae family develop.

The true treasure, however, is beneath the soil: the underground stems and roots forming the famous pungent rhizome. This grows slowly and requires 2-3 years before becoming harvestable. The rhizome has a green exterior and creamy-white interior.

Ideal location

Eutrema japonicum thrives in semi-shaded environments. The plant is uncomfortable in direct, bright sunlight, especially in warm regions. A location with light shade from trees or a north-facing patio is ideal. The plant appreciates humidity and can even thrive in marshy environments. In Japan, wasabi grows along mountain streams. In temperate countries, it is best cultivated as a container plant in a greenhouse or conservatory.

Soil

Wasabi requires highly fertile, moist soil with good drainage. This is a moisture-loving plant that dislikes waterlogging. A mixture of garden soil, peat and sand in a 1:2:1 ratio is excellent. The plant thrives best in slightly acidic to neutral soils. Regular addition of organic matter is necessary. For container cultivation, use nutrient-rich compost with added moisture retention.

Watering

Wasabi requires copious water, especially when the rhizome is developing. The soil must remain moist but not waterlogged. In hot summers, you may need to water daily. In container plants, ensure water drains but the soil never dries completely. The plant appreciates misting or humid environmental conditions. In warm environments, additional humidity may be needed.

Pruning

Wasabi requires minimal pruning. Remove dead leaves or stems. Do not cut back the plant as this impedes rhizome growth. If the plant produces flower stalks and you wish to conserve energy for root growth, you can carefully remove them, though this is optional. The plant must direct most energy to underground growth.

Maintenance calendar

Spring: Begin feeding when new growth appears. Water regularly. Summer: Feed monthly. Provide ample water and humidity. Autumn: Gradually reduce watering as growth slows. Reduce feeding. Winter: Minimal watering. Plant may become semi-dormant. Early spring: Check for pests and begin feeding.

Winter hardiness

Wasabi is frost-tender but can partially survive in temperate climates. Above-ground parts may suffer frost damage, but the root can survive in well-mulched, dry conditions. In the UK and northern regions, cultivation as a container plant with overwintering in a cool greenhouse or protected location is recommended. The plant grows best at temperatures between 8-18 degrees Celsius. Temperatures above 20 degrees can diminish rhizome quality.

Companion plants

Wasabi pairs well with other moisture-loving plants in a kitchen garden or vegetable growing area. Try combining with other Asian vegetables or herbs such as ginger or green tea. In semi-shaded environments, it functions well alongside ferns or other shade-tolerant plants. The plant adds interesting Japanese character.

Closing

Cultivating wasabi at home is a unique experience and provides you with genuine gourmet quality. The plant requires considerable attention and patience, but rewards you with an annual harvest of authentic Japanese wasabi rhizome. This is not as simple as many vegetables, but for culinary enthusiasts it is incredibly rewarding. For seeds or plants, seek specialist suppliers of exotic plant material. The plant is less commonly found in standard garden centres, so online sources are more likely.

Want a genuine wasabi experience? Begin with this fascinating plant!