Potting soil, also known as potting mix or miracle soil, is a medium in which to grow plants, herbs and vegetables in a pot or other durable container. The first recorded use of the term is from an 1861 issue of the American Agriculturist.
Fertiliser (in the form of compost; i.e. leaf mold, bark compost or recycled mushroom compost) is generally not added (or only in very small quantities) for potting soil used for cuttings and seedlings as large amounts of fertiliser are too aggressive for them. It is used for larger plants (larger pots) though.
The use of peat is controversial since the harvesting of peat moss from peatlands (which includes unique habitats such as bogs and fens) degrades 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. Also, the removal of the layer of CO2 absorbing plants releases CO2 into the atmosphere, contributing to climate change.
Different mixes for different uses and plants
For seed starting and cuttings, a mix can be made using 40% coconut coir or peat moss with limestone, 40% vermiculite, and 20% sand. Besides sand, it is also possible to use perlite, using near-similar sized percentages (33%-33%-33%). 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, often with less than 20% of peat moss or other fine-grained materials.
Plants also require potting soil that is specific for their environment.
For example, an African violet would grow better in potting soil containing extra peat moss.
Cacti and succulents require sharp drainage, thus requiring a much larger percentage of perlite or sand.
Commercially available potting soil is sterilized, in order to avoid the spread of weeds and plant-borne diseases. It is possible to reuse commercial potting soil, provided that the remnants of plant roots, fungus, weeds and insects are removed from the mixture through heating before new planting can take place. Packaged potting soil is sold in bags ranging from 5 to 50 pounds (2.3–22.7 kg).
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- Peat moss: Good for plants but bad for the planet?
- Peat alternatives in the garden
- Alternatives to peat
- DIY Potting Soil: 6 Homemade Potting Mixes
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