They grow best in fertile, wet, well-drained soil with a lot of mulch. In commercial planting, seeds are planted 45 cm (1.5 ft) apart and 2.5 cm (1 in) deep. The sunflower is the state flower of Kansas. Sunflower “whole seed” (fruit) are sold as a snack food, after roasting in ovens, with or without salt added. Most sunflowers are remarkably tough and easy to grow as long as the soil is not waterlogged. It’s best to sow sunflower seeds directly into the soil after the danger of spring frost is past. Sunflowers may also be used to extract toxic ingredients from soil, such as lead, arsenic and uranium.