These guidelines have been written to help composters who want to supply the horticultural growing media market meet the quality standards required by this sector. 

Key points:
  • Compost provides major and minor nutrients and increases chemical buffering and water holding capacity in the growing medium in a similar way to loam
  • Compost may assist in the suppression of some plant diseases because it is more biologically active than other growing media constituents
  • Compost may reduce the growth of liverworts, moss and algae when used in blends that retain a drier surface than 100% peat mixes


They have been produced by ADAS , Earthcare Technical and WRAP in consultation with the growing media sector, composting industry, and the Organics Recycling Group (ORG), which is part of the Renewable Energy Association (REA). The guidelines will help a composter manufacture compost with the most suitable characteristics for use in growing media. They are not intended to be prescriptive; the actual detailed specification for compost will need to be agreed with the growing media manufacturer or grower who is purchasing the compost, and will depend on the types of plants to be grown in the mix it is used for. Quality compost is already being used as a constituent of many retail growing media products (for example in reduced peat/peat free ‘multi-purpose compost’ and ‘grow bags’) and is also being successfully used by some professional growers, particularly for hardy ornamental plants. 

Only the highest quality composts with consistent physical, chemical and biological characteristics are suitable for use in horticultural growing media and this document offers guidance on the properties of suitable composts. Regulatory requirements should always be adhered to and are subject to change. Composters/manufacturers/users should ensure that they are always up to date with current regulatory requirements. All composts destined for use in growing media should be produced and used in accordance with current regulations and already be produced in accordance with the requirements of BSI PAS 100 and the Compost Quality Protocol (the latter is not applicable in Scotland).

The Compost Quality Protocol (CQP) was launched in 2008 and revised and re-published in 2012. It defines when compost is considered a product, and no longer falls under the waste management regulations. One of the requirements of the CQP is that composts are produced to a recognised standard e.g. BSI PAS 100. (NB. Compliance with the Compost Quality Protocol is not required in Scotland at the time of publication however as part of Scotland’s end of waste position statement, SEPA requires that compost is produced to BSI PAS 100).

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