40-60 Days to maturity. Brassica rapa var. Pekinensis 'Osaka Shirona'. Osaka Shirona Chinese Cabbage Seeds. Annual. The shirona Cabbage group may be a cross between Chinese cabbage and pak choi, sometimes listed as Komatsuna. It is both cold and heat tolerant making it ideal for regions with a range of temperatures throughout the growing season. Osaka Shirona is a great loose-leaf variety that is more attractive than headed varieties and can be harvested anytime from the microgreen stage to full maturity. ~ 11,400 seeds per oz.