Florida's soil developed from limestone over thousands of years, as the region once formed the bottom of a shallow sea. In South Florida, the region generally south of the line from Fort Pierce to Sarasota, the soils remain neutral to alkaline in pH, especially if little decaying organic matter is present. The soil profile changes locally across the region, depending on parent rock material or the presence of natural vegetation.
Parts of Miami-Dade and Monroe Counties in the southernmost reaches of the state contain rocky or gravelly soil, which is coarse ground that drains freely after the frequent summertime rains. According to the University of Florida, percolating rainwater, over many years, dissolved the rocks into softer, more loamy or sandy soils in small areas called "solution holes." Here, an increase in native plants, typically called pinelands, grow, contributing organic matter to improve the fertility and texture of the gravelly loam and sand. These rocky soils are sometimes called Krome or Rockdale soils.
A vast expanse of South Florida's interior contains sandy soil. Left over from the erosion of limestone and deposits from the shallow ancient sea, local variations exist with different amounts of organic matter in the top 1 to 2 feet of soil. Sandy loams exist in western Palm Beach County, now a sugarcane agricultural hotbed, and pockets of barren pure sand also exist across the region, especially near the coast. The Florida Native Plant Society mentions that pure sand generally fails to have any surface profile and can be fully dry or constantly inundated with water, depending on elevation or proximity to the water table. Addition of decaying plant debris improves the texture, fertility and water-retaining properties of sand.
The common soil in the Everglades is marl soil. Rich in calcium and also referred to as a calcareous soil type, marl soil is most common in Miami-Dade and Monroe Counties. Marl occurs in low elevations that seasonally go underwater for summer and autumn months and then dry out in the winter and spring. Organic matter from plants accumulate atop the marl soil when underwater, eventually creating a mucky to moist loam soil 2 to 72 inches deep atop a hard limestone bedrock. Rich in humus or peat, marl soil drains slowly. Common natural vegetation associated with marl soil includes black mangrove, buttonwood, switchgrass and sawgrass. Biscayne soil is a type of marl soil.