Even after the introduction of machinery, sugar production, once requiring the effort of thousands of slaves, remained a highly labor-intensive process. A grass ranging from one-half inch to three inches in diameter and reaching up to twenty feet in height, sugarcane grows best in tropical climates and needs plenty of natural rainfall or irrigation. The growing season lasts eight to thirty months, depending on weather conditions. The longer the season, the more sucrose-laden the crop becomes. Rather than using seeds, growers replant cane using cut pieces of stalk, which when buried in soil sprout new growth.