Tatsoi is is a non-heading mustard that is very similar in flavor to bok choi. Tatsoi plants tend to grow in a flatter rosette than bok choi, with long, spoon-shaped leaves. As with most of the Asian greens, it grows quickly, with few problems. Tatsoi is a biennial in growing zones 4 ? 7. If planted in the fall, it will overwinter with protection and resume growth in the spring. The plants will bolt (flower and set seed) as warm summer weather sets in.. Leaves that are harvested when they are young and small taste like spinach. Mature leaves have a tangy mustard flavor. You can use them any way that you use bok choi or napa cabbage. Tatsoi leaves are most frequently used raw in salads or cooked in soups and stir fries. Like its cousins, tatsoi prefers partial shade. It only needs 3 to 5 hours of sunlight daily. You can grow it in full sun if you keep it well-watered. If the plants start to dry out, they will bolt, i.e. flower and then set seed.