21 days in summer or 50-60 days in winter to maturity. Brassica rapa var. perviridis. Summer Fest Komatsuna Mustard Seeds. Non-GMO, warm or cold-season, annual, hybrid. This popular traditional Japanese hybrid komatsuna has glossy, thick dark green leaves and an upright growing habit. Summer Fest is an extra early komatsuna that is resistant to heat. It is especially suited for summer cropping and has a high tolerance to multiple diseases. Komatsuna is extremely underrated in the west. The summer fest variety is particularly well-suited for summer production. Approx. 10,600 seeds per ounce.