Histosols are soils that are composed mainly of organic materials. They contain at least 20-30% organic matter by weight and are more than 40 cm thick. Bulk densities are quite low, often less than 0.3 g cm3.

Most Histosols form in settings such as wetlands where restricted drainage inhibits the decomposition of plant and animal remains, allowing these organic materials to accumulate over time. As a result, Histosols are ecologically important because of the large quantities of carbon they contain. These soils occupy ~1.2% of the ice-free land area globally and ~1.6% of the US.

Histosols are often referred to as peats and mucks and have physical properties that restrict their use for engineering purposes. These include low weight-bearing capacity and subsidence when drained. They are mined for fuel and horticultural products.

Histosols are divided into 4 suborders: Folists, Fibrists, Saprists, and Hemists. Click here for more information about these suborders. Click here to view a map of their distribution in the US.