Carrot. Planting: Carrots (Daucus carota) are cool-season plants that grow best at average temperatures between 60 and 65 °F. The optimum soil temperature for seed germination is 55 to 75 °F. Seeds will not germinate above 95 °F.lant radish seed in rows 12 to 24 inches apart and place the seed ½-inch deep with about 1 inch between seeds. Radish can be broadcast-seeded in a 12-inch bed and then thinned when plants are in the one to two true leaf stage.