The sunflower is the state flower of Kansas. That is why Kansas is sometimes called the Sunflower State. To grow well, sunflowers need full sun. They grow best in fertile, wet, well-drained soil with a lot of mulchThe sunflower (Helianthus annuus) is an annual plant in the family Asteraceae, with a large flower head (capitulum). The stem of the flower can grow up to 3 metres tall, with a flower head that can be 30 cm wide.