Wheatgrass is a natural source of vitamins and minerals (a few of which are antioxidants) including: 1  Vitamins A, E, and B-12. 2  Calcium. 3  Selenium.4  Magnesium. 5  Iron.heatgrass is a natural source of vitamins and minerals (a few of which are antioxidants) including: 1  Vitamins A, E, and B-12. 2  Calcium. 3  Selenium.