Yu Choy Sum Seeds - Jung Green. Heirloom, Non-GMO. Brassica rapa var parachinesis. 40-45 days. Warm season annual. 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.) ~ 10,000 seeds / oz. Yu Choy Sum Seeds - Jung Green This choice, medium maturing Yu Choy Sum variety produces dark green leaves and is tolerant to heat and suitable for summer and fall season. Prepare fertile, well-drained soil. Sow seeds in a sunny location in summer or fall. Keep soil moist. Fertilize as needed. Yu Choy Sum is very sensitive to temperature. Exposure below 50-55°F for two weeks may result in bolting. Optimal growth temperature range is 60-80°F. Lightly steam, stir-fry or pickle. About 10000 seeds an ounce. Seeds Per Package: 3 g packet - Approximately 1,000 Seeds