What’s in your compost?
With no ingredient list on compost bags, it’s often hard to tell if they contain peat or not, or what else may be in them...
The exact recipe for each potting compost is a closely guarded secret. But most composts rely on the same basic ingredients. If you want organic compost, look for those with Soil Association accreditation, and if you want to avoid peat, choose composts clearly labelled as peat-free.
Basic ingredients:
■ Peat Mechanically harvested from 10,000-year-old peat bogs, it’s cheap and reliable for growing plants, but non-renewable, with high carbon emissions.
■ Coir A by-product of the coconut industry, coir is light, fibrous and absorbent. But it’s shipped from South Asia, which generates pollution, and processing it uses lots of water in a region where water is in short supply.
■ Wood fibre Produced in the UK, wood fibre is lightweight and renewable. However, it takes a lot of energy to harvest and transport it, and it’s in short supply.
■ Bark This unwanted by-product of the forestry industry is sustainable and good for biodiversity, but heavy to transport.
■ Composted green waste Made from recycled garden waste, locally produced, and the most eco-friendly of peat substitutes. But the content is variable, so manufacturers use it with caution. And it’s heavy to transport.
Other ingredients in some composts:
■ Loam – non-renewable, energy-intensive to produce and heavy to transport.
■ Bracken or wool – locally produced, cheap, lightweight and sustainable.
■ Slow-release fertiliser – either synthetic or organic.
■ Perlite – non-renewable, as Q it’s mined from volcanic rock.