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There are a number of issues to consider when selecting potting soil. Learning how to read the information on potting soil packaging can be very helpful, as it will provide clues about the composition and quality of the soil. Generally speaking, most plants do well with a generic potting soil, but some may have special needs. For plants like orchids and bromeliads, many companies make potting soils specifically designed for those plants, and they will often be labeled with terms like “orchid mix” to make them easy to find.
The growth medium used for a plant has tremendous impact on plant health. Potting soils are made by mixing peat moss or other moisture-retaining substances, vermiculite or pearlite for drainage, and organic matter like compost for nutrients. Most plants like medium to rich, well-drained soil with a neutral pH. Generic potting soils are made to this formula, and people can adjust the soil slightly with soil amendments to make it richer, change the drainage, or alter the pH. Plants may have a specific preference for peaty, loamy, or sandy soil, in which case people need to use appropriate potting mixes or buy additives to mix with potting soil.
Organic potting soil includes organic soil amendments like compost, produced without the use of pesticides, herbicides, and antibiotics. This can be important to people who want to maintain an organic garden. Other potting soils may have been treated with fungicides, antibiotics, and other compounds to reduce the growth of harmful organisms. Another thing to look for when choosing potting soil is whether it contains beneficial fungi. Many soils have mycorrhizal fungi mixed in to promote root health.
For plants like cacti, succulents, and other plants adapted to dry environments, it is important to find a very well drained potting soil, with less peat moss and other additives that may increase moisture retention. For tropical plants and plants adapted for swamps, high moisture retention is desired to keep the plants healthy. Other plants can benefit from a neutral mix of ingredients. For plants like orchids, bromeliads, and other epiphytes, an epiphyte medium is needed. These potting media are designed for excellent drainage to avoid keeping roots soggy and use materials like chipped bark.
The packaging on potting soil should indicate the composition of the mixture. Higher vermiculite or pearlite equals better drainage, while higher moss content means more moisture retention. If the soil is specifically formulated for particular groups of plants, this information will be provided as well and can be useful for people looking for soils to satisfy finicky plants.
Many nurseries and garden centers are happy to assist customers who may be overwhelmed by the choices in the soil department.