The aim of this study was to compare vitamin C and β-carotene contents in cruciferous vegetables (Brassica oleracea) grown under diversified ecological conditions for three consecutive years. The hypothesis to be verified was that statistically, vitamin C and β-carotene contents in cruciferous vegetables from the closest areas around a steelworks, organic farms, and randomly purchased in retail differed significantly, independent of the climate and agro-technical conditions. The study was done on three species of cruciferous vegetables: ‘Stone head’ white cabbage, ‘Langedijker’ red cabbage, and ‘Dolores F1’ Brussels sprouts. All these species of cruciferous vegetables were characterized by significantly higher vitamin C and β-carotene contents (Brussels sprouts) when grown on organic farms vis-à-vis vegetables grown around a steelworks or available in retail in Kraków, which may be evidence of efficient organic growing technology, and may indicate another way to improve the quality of food.