An ideal cool-weather crop, radishes develop spicy bulbs during the chillier months of spring and autumn. Arrange the seeds at least an inch apart in half an inch of loose, moist, and well-lit dirt. They'll grow fast: Certain radishes may be ready for harvest just 22 days after planting, although other varieties may need up to 70. Once yours begin sprouting leaves, thin out the rows by plucking every other radish. A new row may be planted in early spring or late summer, depending on when you plan to dig your vegetables up and eat them.