Rhubarb performs best in well-drained, fertile soils that are high in organic matter. Heavy, clay soils can often be improved by incorporating organic matter, such as compost or well-rotted manure, into the upper 12 to 15 inches of soil. The planting site should also receive at least 6 to 8 hours of direct sun each day. Avoid shady sites near trees and shrubs.
Learn more about rhubarb in this article: Growing Rhubarb in Iowa