Peat is harvested from natural peat bogs. It is partially decomposed sphagnum moss and plant material which forms in layers in acidic and anaerobic conditions (without oxygen).

Pros

Cons

It is a sterile growing media – it does not contain harmful algae, pests or weed seeds. It is not expensive. It has an excellent water holding capacity (it holds a lot of water like a sponge). It has an excellent pH buffering capacity (it does not quickly turn more acid or alkali when substances such as fertilisers are added to it). It is relatively easy to handle as it can be compressed into bales, wrapped in plastic and loaded onto pallets.

Peat use is very bad for the environment – removal of peat bogs strips away extremely fragile and important habitats and releases carbon dioxide into the atmosphere. Many garden centres will not now stock plants grown in peat and so growers who wish to sell to these garden centres must find an alternative growing medium. Legislation will soon come into place which prevents the horticulture industry using peat entirely.

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Coir is a natural fibre taken from the outer husk of coconuts. It is pre-treated by being soaked in a calcium solution to remove natural sodium and potassium salts which are high in the pith and then fluffed up and bashed in a mechanical tumbler to break the fibres apart.

Pros

Cons

Very light weight and easy to handle when dry. High water holding capacity like a sponge. It is a by-product of the coconut industry. It can be reused. It provides good aeration. It is relatively inexpensive. It is lightweight to ship.

Some sources are contaminated with algae. It is heat treated before sale which is highly energy intensive. Some sources are particularly high in potassium salts and although potassium is required by plants for growth, if quantities are too high then plants stop being able absorb magnesium effectively, the salt itself can also be an issue if the coir is not properly treated. High carbon footprint when shipped to countries which cannot grow coconuts

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Compost made from decomposing organic waste such as kitchen waste and garden weeds. This can be produced on a home scale for home garden use or on a commercial scale. Some cities provide wheelie bins for garden waste which are then collected and composted to produce excellent compost for sale.

Pros	Cons
High in nutrients. Excellent pH buffering. Excellent water holding capacity. The most natural product apart from soil. Often inexpensive. Usually can be made at home or purchased relatively locally, at least in the same country.	Some producers mix in composted woodchip which makes the compost have an open texture, great for improving soils, but too open for small pots as it dries out too quickly. It can smell stronger than other compost types. It is more variable than peat or coir based composts so when producing large batches of plant commercially there can be variations in growth rate.

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There are a range of branded peat free options, most of which are mixes of growing media such as coir, composted wood chip and wood fibre.

Pros	Cons
Much lower environmental impact than using peat. Pre-mixed formulas are created specifically for tasks such as seed sowing which makes a reliable compost. Available in easily handled bags from local garden centres and commercial suppliers.	Relatively expensive. Some of the ingredients, for example coir, may have a high carbon footprint from being imported. A relatively new product so not extensively trialled.

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When wool prices are low, sheep’s fleeces are composted to produce a growing media.

Pros	Cons
Releases nutrients – wool is particularly high in nitrogen and potassium compared to other compost materials and also contains several trace elements essential to plant growth. Can be mixed with other substrates such as coir or bracken compost to improve structure and water holding capacity. It is a by-product of the farming industry.	Expensive. Can be difficult to source. It produces a pungent odour in warm damp greenhouses and polytunnels which can create an unpleasant working environment.