Yu Choy Sum Seeds - Early Green. Heirloom, Brassica rapa var parachinesis. Non-GMO. Warm season annual. 30-40 days. Flowering Brassica is a fast growing green that can be harvested as Yu Choy (stem and leaf) or Yu Choy Sum, (stem, leaf and flower buds.) This high quality, early maturing variety is developed for growing baby Yu Choy or Yu Choy Miao. ~ 19,000 seeds / oz.