Organic Soils Organic soils are defined in the Canadian System of Soil Classification as soils that have developed largely from organic deposits. Most Organic soils develop under saturated conditions and are derived dominantly from vegetation that grows in poorly and very poorly drained areas. Organic soils contain > 17% organic C (>30% organic matter) by weight and have a specific depth, degree of decomposition and properties in the middle tier (40 to 120 cm). These soils must have Of (up to 60 cm thick), Om (up to 40 cm thick), or Oh (up to 40 cm thick) organic horizons. Up to 40 cm mineral material is allowed to be present in a soil that is classified as Organic soil as long as organic material is at least 40 cm in thickness.