23rd July 2021
Many have argued for the last two decades that we should stop using peat in compost, but the climate-change crisis has highlighted the role that peat plays in adding carbon dioxide to the atmosphere.
The Committee on Climate Change estimates around 39 tonnes of carbon dioxide has been released from every hectare of lowland peat that has been drained and fertilised every year. While a further 18.5 to 23 million tonnes are released from other peatlands in the UK.
Peat is an accumulation of partially decayed vegetation or organic matter, created from sphagnum mosses growing in bogs. It accumulates at a rate of 1-2mm per year and is harvested for use in compost and burning in electricity generation.
Peat acts as a carbon sink, locking in large amounts of carbon. To harvest it for use in compost, the bogs are drained and cleared of all vegetation. Harvesting not only removes around 20cm layer of peat every year, in other words, a century’s worth of peat accumulation, but allows the exposed peat to oxide, releasing carbon dioxide.
Peat bogs are also an invaluable habitat for flora and fauna, supporting many rare and vulnerable native species not found anywhere else. Peat extraction wipes out the entire eco-system and although habitat regeneration schemes are now being attempted, there is no guarantee these will succeed. Peat bogs also create natural flood defences, soaking up excess rainfall and releasing it slowly.
Compost manufacturers have missed successive deadlines for the end of peat compost. However, they are now under increasing pressure to reduce the percentage of peat in their products, and, ideally, to replace it with peat-free products. As a result, one major peat producer has stopped harvesting peat in Ireland, while manufacturers, retailers and representatives from commercial horticulture are preparing a roadmap to the end of peat use.
The good news is there are an increasing number of peat-free composts available to gardeners and the percentage of peat in composts is also dropping. A few years ago, most peat composts contained around 70% peat and this has now reduced to around 45%.
Peat-free composts are typically made up from materials such as wood fibre, composted bark, coir and, to a lesser extent, composted garden waste. However, you can also find composts containing sterilised soil, vermiculite, perlite, grit and manure. There is even one series of composts made from composted bracken and sheep’s wool. It’s likely new materials will be used as peat-free composts become the norm.
Wood fibre can be the shavings taken from lumber yards as timber is sawn into planks. However, more often it is treated. Chipped wood is wetted, pressurised and heated to turn it into a light, fluffy material. The result is a little akin to putting a woolly jumper in a tumble dryer: the fibres expand and split apart, making them better at holding air and allowing water to drain freely.
It's increasingly used in both peat and peat-free composts and typically makes up around 50% of the total volume. Wood fibre can lock up nitrogen, leaving plants starved of this vital nutrient, but manufacturers usually balance the fertiliser to get over this problem.
Composted bark is typically made from the bark of conifers felled for timber. It's mostly sourced in the UK and is a by-product that wouldn't be used otherwise. It's milled to small pieces and the composted until it has leached any tannins and is inert.
Coir is a fibrous material made from coconut husks and is milled to make a peat-like material for horticultural use in areas of India and Sri Lanka.
It’s often mixed into peat-free composts, making up about 5-20% of the total, but you can also buy it on its own as a compressed block. It expands into a fluffy compost when water is poured onto it.
Coir is widely described as being environmentally friendly as it's a naturally occurring product that would go to waste if it weren't used in composts. However, there are several issues, including the amount of water needed to rinse salts from the coir, as it's produced in areas where clean water is scarce. Manufacturers are working to mitigate this with water collection and storage during the rainy season.
In the past, peat-free composts were largely made from green compost, but it’s becoming less common due to problems with its variability and nutrient balance.
It’s a widely available and cheap material as it’s made from the green waste collected by local authorities or from municipal waste sites. In other words, it is very similar to the contents of your compost bin, but with notable differences, including:
Some manufacturers have now decided not to use any composted green waste in their composts and are using wood fibre instead. Other producers have altered where they source the materials for their green compost and have refined their composting process to ensure a good-quality product.
Getting used to peat-free composts can seem daunting, but with a little care you should get very good results.