TOPS Learning Systems Life Sciences, grades 3-8. Radishes aren't fussy. Provide them with a covered, moist towel, and away they grow. In just a day the seeds will sprout. By the end of the week you'll get sprouts one or two inches tall. Because radishes grow so fast, tropisms are easy to see roots grow toward water, leaves tilt toward light, stems bend against gravity. Kids will draw, measure and graph growth, eat a tiny sun salad, study toxic stress!