Wasabi Japonica 'Mephisto Green' - Cotswolds Grown Culinary Herbs

An unusual and highly sought-after edible plant, Wasabi japonica ‘Mephisto Green’ produces large, heart-shaped leaves and thick stems, but it’s the knobbly rhizome that is most famously used to make authentic wasabi paste. This variety is specially bred for increased cold tolerance and robust growth, making it more suitable for UK gardens. Thriving in cool, shady, and damp conditions, it’s a fascinating addition to a shady border or water garden.

Wasabi japonica ‘Mephisto Green’, commonly known as Wasabi, is famed for its culinary use and lush foliage. In the right conditions, it forms a striking ornamental edible that doubles as a conversation starter in the garden.

 

Perennial

Clump-forming, Edible rhizome and foliage, Shade-loving

Flowers: March – May (small white flowers, sometimes removed to preserve energy for rhizome growth) Foliage: Year-round in mild conditions; may die back in winter and regrow in spring

Scientific Name
Wasabi japonica ‘Mephisto Green’ (a cultivar of Eutrema japonicum, often still referred to under the older name)

Synonyms
Eutrema japonicum

Common Name
Wasabi, Japanese Horseradish

Origin
Mountain stream beds of Japan – native to cool, shady, moist habitats

Pruning Tips
Remove any yellowing or damaged leaves regularly. Flower stalks can be pinched out to encourage root development if growing for harvest

Wildlife Value
Minimal wildlife value, though dense foliage may offer shelter to insects

Positioning
Part to full shade in a cool, sheltered spot – ideal near a pond, bog garden, or north-facing wall. Avoid hot, dry, exposed sites

Water
Requires consistently moist soil – never allow to dry out. Likes damp, but not waterlogged, conditions

Soil
Rich, humus-rich, moisture-retentive but well-draining soil. Mulch to keep roots cool and moist

Food
Feed monthly in spring and summer with a nitrogen-rich liquid feed for leaf growth, then switch to a balanced fertiliser to support rhizome development

Pet-safe
Generally considered non-toxic, though spicy rhizomes and leaves may irritate pets if consumed

Sprouts Top Tips
For best rhizome development, grow wasabi in a large pot sunk into a shady, damp area of the garden. Rhizomes can take 18–24 months to mature, but the leaves and stems are also edible in the meantime.