Red colors often indicate iron accumulation or oxidation in oxygen-rich, well-aerated soils. Iron concentrations caused by redox reactions in periodically saturated soils may also present red colors, particularly along root channels or pores.

Red soils include multiple soil types (e.g. ultisols, alfisols, oxisols) that are classified as red soil when they develop a distinct reddish color, which can vary from reddish brown to reddish yellow due to their high iron content.

“Reddish and red-brown soils come in a range of hues, but picture the red rocks of the Western U.S., a burnt, rusty red,” Niewold says. This soil may have a lot of the iron oxide hematite. It’s usually acidic, low in calcium and high in clay. If it’s darker, that may mean more organic matter and less drainage.