Napa Cabbage Growing Information Brassica rapa var. pekinensis Transplant: Start in trays at ¼” deep. Transplant 3-5 weeks from seeding date, after last frost. Can also be direct seeded after last frost. Soil temperature for germination is 55-75° F. Spacing: 12-15" apart in rows that are 24-30" apart. Growth needs: Napa is a cool-season crop prone to bolting in warm temperatures and when young plants are exposed to fluctuating temperatures. Best planted as day length decreases. Monitor for bolting. Harvest: When heads are dense, and before bolting is initiated. Storage: Can store at 36° F at 95% relative humidity for 4-6 weeks.