Horseradish and wasabi both belong to the same botanical family, Brassicaceae.
Horseradish (Armoracia rustieana) is a hardy perennial that forms a rosette of long leaves. The 30 or more strains in cultivation include 'Bohemian; 'Swiss' and 'Sass,' and almost all of them are sterile. There are two ornamental forms - one is variegated with white, the other has purple-suffused leaves. Belowground, horseradish forms a taproot that expands in diameter in the second and third year.
Native to Japan, wasabi or Japanese horseradish (Wosabiajapónica} is a semi-aquatic perennial with long-stemmed,
heart-shaped leaves. Its inflorescences of white cruciform flowers reach 16 in. (40 cm). There are a number of varieties, including 'Tainon No. 1' and 'Daruma; but all form thick, knobbly rhizomes.
• Position Horseradish requires a sunny position and a well-dug soil enriched with rotted compost. Grow wasabi in very clean, cool, slightly alkaline running water, with plenty of shade. The temperature should be between 50 and 55°F (10°C and 13°C).
• Propagation In spring, plant pencil-thin sections of lateral horseradish roots horizontally, or up to an angle of 30° from the horizontal. Cover with soil, and firm down. Propagate wasabi from offsets of the rhizome.
• Maintenance Don't let horseradish dry out, or the roots will become bitter. Keep wasabi well-shaded, cool and watered.
• Pests and diseases A number of leaf-eating insects can be a problem for horseradish. White rust, Alternoria and bacterial leaf spot may occur.
• Harvesting and storing Dig up horseradish roots and use them fresh at any time in the second and third year; they are at their peak in flavor after the first frost. Store clean roots in sealed plastic bags in the refrigerator for up to 2 months.
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