Do pinto beans grow better in soil or in cotton? Most seeds start in dirt. But cotton holds moisture without packing down the way soil can. You plant pinto beans in four different materials: - nursery potting mix - local dirt - a blended soil - plain cotton balls Each material gets three cups with one bean each. You water every cup the same amount every other day for six weeks. At the end of each week, you measure how tall each plant has grown. The results show which material gives pinto beans the best start.