Brassica oleraceae var. chinensis. Dark-green leaves are supported by thick, sweet, white stalks that are mild and juicy with a delicate flavour. Joi Choi pac choi seeds can be planted in cool soil and grow to 45cm (18") tall. Space plants 60cm (12") and be ready to harvest promptly. Cover with cloche if planting in very early spring, as plants will bolt if seedlings are exposed to cold temperatures. Sow numerous times at two to three week intervals to enjoy a long harvest window, and to avoid the whole crop maturing at once. The mature plant is somewhat cold-hardy; sow again in late summer for fall and winter harvests.