30 to 40 Days to maturity (warm climates), 50-60 Days to maturity (cold climates). Brassica rapa var. perviridis. Green Boy Komatsuna Mustard Seeds. Cool-season annual hybrid. Komatsuna is an easy-to-grow, mild-tasting mustard variety. Its flavor profile tastes like mild Asian mustard and spinach. It is a cool-season annual hybrid variety known for its cold tolerance, though cold temperatures will slow growth a bit. It can be grown throughout the year in areas with mild temperatures. Try growing in greenhouses or homemade hoop houses during the winter. Approx 11,250 seeds / oz.