Komatsuna Mustard Seeds - Summer Fest - Hybrid. Non-GMO. Brassica rapa var. perviridis. Alt names: komatsuna, mustard spinach, tender green mustard. 21 days in summer, Warm season annual. 50-70 days in winter. This popular traditional Japanese komatsuna hybrid has glossy, thick dark green leaves and an upright growing habit. Apx. 10600 seeds per ounce.