(Brassica napus) This cabbage relative is grown for its roots, which are similar to turnips, but larger, sweeter and milder. Rutabagas are believed to have originated in Russia, and they were first mentioned by a Swiss botanist who observed them growing wild in Sweden in the 1600s. Rutabaga requires a longer season, 90-120 days, but can tolerate cool temperatures as it matures, and is at its best harvested in late autumn. Sow about 90 days prior to expected fall frost, in rich, deeply worked soil of average fertility. Rutabaga likes soil that is rich in potassium and has been amended with potash. Ideal germination temperature is 60-70F. Seeds germinate in 7-10 days. Sow seeds 1/4 inch deep. Thin to about 6-8 inches apart, control weeds and keep moist. The leaves of some varieties make passable greens when harvested young.