50 days. Non-GMO, Heirloom Tatsoi Mustard Herb Garden Seed from True Leaf Market. Brassica rapa subsp. narinosa. Tatsoi Mustard or "Spoon Mustard" comes from China and gained tradition as a tender culinary herb in Japan. As a relative to bok choy and Chinese cabbage varieties, Tatsoi Mustard is a cold-hardy biennial with active growth that can overwinter in regions with mild winters! This rounded no-heading mustard often called "Tat Choy" is a popular savory dish with "spoon-shaped" forest-green leaves that can be sauteed, steamed or fried with rich seasoning.