(Image from: https://hudsonvalleyseed.com/products/tatsoi?_pos=1&_sid=1273e44d8&_ss=r)
Growing Instructions for Tatsoi:
Sow indoors beginning 8-10 weeks before last frost, or direct sow beginning 3-4 weeks before last frost. Can be sown straight through until September, though spring sowings can bolt early and be taken by flea beetles; consider using row cover. Sow more densely than indicated for baby clippings. Harvest whole head—not an ideal cut-and-come-again green. Superb in fall and winter.
(from Hudson Valley Seed Company website)