Soils are essential for life on earth and critical in many environmental challenges facing the earth. For example, most plants depend on soils as a suitable medium for growth by providing at least six factors for plant growth: physical support for anchoring the root system, aeration, and ventilation for the roots, pores for absorbing rainwater and holding it for use by the roots, moderation of temperature fluctuations, protection from phytotoxic substances, and supplying inorganic minerals in the form of dissolved nutrients.
The four major soil components are air, water, mineral matter, and organic matter. An ideal soil for plant growth has a composition by volume of 50% solid (45% mineral, 5% organic) and 50% pore space (25% filled with air and 25% filled with water).
The most important consideration in making potting soil for succulents is that it will drain well. The soil must be porous so that water penetrates easily and drains away quickly. Rapid exchange between water and air is essential at the roots but cannot happen when water is excessive. A soil that remains wet for long periods can quickly kill most succulents.
There is no one way to prepare a soil mix for succulents, and any that drains well should support healthy plant growth. By experimenting, you can find the one that works the best for you. An example of a good soil mix for succulents is two parts by volume of potting soil: 1 part perlite and 1 part small-size gravel, e.g., pumice, turface, or crushed granite. Even simpler is a 1:1 mixture of potting soil and perlite. If sand is added to a mix, it should be coarse-grained such as building sand. The addition of organic material is not necessary since, in their native habitats, most succulents live in weathered soils, which are very low in humus.
A soil mixture for succulent plants should have a good crumbly structure. To test your soil mix, moisten and squeeze with your hands: the mixture should not form a lump but crumble loosely.
Often it is recommended to repot your succulents every couple of years. Using an appropriate soil mix will promote their good health and keep them looking their best.
- Succupedia: Browse succulents by Scientific Name, Common Name, Genus, Family, USDA Hardiness Zone, Origin, or cacti by Genus