The Role of Peat in Assuring the Quality of Growing Media

Producers and users of growing media are exposed to high risk if significant quantities of potentially unsuitable ingredients are included in the product. Combined with economic reasoning, this dictates that the constituents of growing media should possess as many suitable characteristics as possible. Sphagnum peat has been the most important growing medium constituent for many decades because its properties are the best available. The use of other organic and mineral-organic materials is being forced ahead by research and development against a background of public favour for peat replacement, recycling and re-use of biodegradable waste. Considerably more resources have been invested in the testing of peat alternatives than in peat itself during recent years, and the utility of a large number of alternatives has been assessed. Most candidate materials are only slightly or not at all suitable for use in growing media. The exceptions are composts, wood fibre products, bark and composted bark, and coir. These have become established, to a greater or lesser degree, as reliable substrate constituents. Their manufacture, characteristics, advantages and disadvantages are reviewed. A continuing need for peat as a constituent of growing media, at least for dilution purposes, is foreseen. Thus, increased imports of peat and growing media to countries with intensive or expanding commercial horticulture and inadequate domestic peat reserves are to be expected in the future.