Characteristics of Soil for Tropical Plants

Oxisol

• Soils are classified into 12 different orders. The order of soil where most tropical plants grow is called Oxisol. These are highly weathered soils with lots of clay that are rich in iron and aluminum minerals. Only about 7.5 percent of the world's ice-free land is covered by this soil order. In the U.S. it only occurs in Hawaii. Even though these soils have low fertility, with added fertilizer they can be productive.

In Nature

• The surface soil of tropical regions is thin and of poor quality. It contains very few nutrients. The main source of nutrients comes from recycling organic matter. Organic matter is the material left behind by decaying plant and animal materials. Because there are so many organisms at work in areas where tropical plants grow, organic matter is quickly broken down and absorbed by the soil. Once the nutrient rich organic matter is broken down, it's quickly leached from the soil by the huge amounts of water tropical plants are exposed to. The soil is usually dense, with a high amount of clay and only a thin layer of organic matter at the top.

In Captivity

• Most tropical plants don't need to grow in soil classified as an Oxisol to thrive. Tropical plants will grow in many different types of soils. The soil must be well drained, i.e., it must allow water to pass through it easily. It must also be fertilized frequently so the plants have the nutrients they need. Frequent watering is also a requirement of any tropical plant no matter what kind of soil it's in. You can use a home potting mix or any other soil mix that has a large amount of organic matter. You might also want to add some sand to a topsoil when growing tropical plants in it.

No Soil Plants

• There are significant amounts of tropical plants that don't grow in the soil at all. Bromeliads and orchids feature thousands of species that don't grow in soil. These plants have evolved to live in the canopy of tropical forests. In captivity the plants are grown in very loose bark and rock materials that serve as a kind of soil. However, these plants get most of their nutrients from air and water. In the wild these plants perch on tree branches and absorb what they need from the abundant environment around them.