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Potting soil or growing media, also known as potting mix or potting compost (UK), is a substrate used to grow plants in containers. The first recorded use of the term is from an 1861 issue of the American Agriculturist. Oxford English Dictionary Despite its name, little or no soil is usually used in potting soil.
Good growing mediums have a number of properties including moisture and nutrient retention capacity, quick water infiltration, pore space for aeration (plants need oxygen), drainage for excess water, decompose slowly, and provide support for the plants growing in them. They also have an optimal range of pH, cation exchange properties, and lack substance that are toxic to plants These are also dependent on the type of plant grown since there is wide variation in moisture and nutrient needs among different plants.
The use of peat is controversial since the harvesting of peat moss from (which includes unique habitats such as bogs and fens) can degrade these peatlands. Peatlands are home to a diverse range of plant and animal species. Peat also has a very slow accumulation rate, as little as 1mm per year, so they take a long time to regenerate. Peatlands are also carbon sinks, constituting 3% of the world's surface but storing up to 30% of the carbon sequestered in the soil. The removal of the layer of absorbing plants releases into the atmosphere, contributing to climate change. Gardeners urged to stop using peat-based compost Peat moss: Good for plants but bad for the planet?
As such, alternatives such as coconut coir are promoted by some organisations. Peat alternatives in the garden Alternatives to peat
Nutrients not supplied by the bulk will need to be supplied by the fertilizer. In conventional mixes they may be slow-release formulae of synthetic fertilizers, while organic mixes will use organic source such as compost (e.g. leaf mold, bark compost or recycled mushroom compost). Overuse of fertilizers will, as with in normal soils, risk damaging the plant. For compost, the maximum recommended amount is 1 part compost to 1 part bulking material.
A soil test may be done to analyze the chemistry of a potting mix, despite the mix not necessarily being made of soil. As an approximation for indoor home planting, the mix is generally treated as greenhouse growth medium. The main method is a saturated media extract (SME), which tests the chemical contents of a water extract of the mix.
For seed starting, a "germination mix" is typically light-weight and suitable for starting small-seeded plants. A "seed starting" mix is suitable for larger seeded crops. Following early growth, most plants prefer a potting mix that is more well-draining.
Cacti and succulents require sharp drainage, thus requiring a much larger percentage of perlite or sand.Burne, Geoffrey. "Encyclopedia of Container Gardening." Page 22. Fog City Press. Carnivorous plants, such as the Venus flytrap and the pitcher plant, prefer the nutrient-poor, acidic soils common to bogs and fens, while water-based plants thrive in a heavier topsoil mix.
As with garden soil, potting soil can attract insects. For example, the fungus gnat is often found around houseplants because it lays eggs in moist potting soil.
Infections of Legionnaires' disease due to potting mix have been reported in Australia, New Zealand, the Netherlands, the United States, and Japan.
+Reference levels for potting mix by the SME method
Different mixes for different uses
The growth medium should be adapted to each plant's (and growth stage's) preference for aeration, drainage, nutrition, and pH. What is Potting Soil?
Sterilization
Commercially available potting soil is sterilized, in order to avoid the spread of weeds and plant-borne diseases.
See also
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