Peat-free growing?

Peat is partly decomposed plant and bryophyte material, and is usually >60% organic matter compared to 1-6% organic matter in mineral soils. Decomposition is slowed by the prevailing anaerobic conditions of the waterlogged habitats where peat is formed, often taking hundreds of years for peat to develop to any significant depth. For centuries, lowland peatlands were drained and/or peat extracted largely for fuel, and the land then used for agriculture or forestry. This escalated from the late 1940s, with the more inaccessible upland peatlands then targeted by drainage and other land management initiatives to improve grazing pasture and habitat for game birds. As a result, the UK and Ireland have lost or severely degraded much of their peatland habitats.

Commercialised growing media first became widely available in the UK in the 1930s, based on the John Innes mixes of loam, peat (25% of mix), sand and added fertilisers. However, it wasn’t until the 1960s and 1970s, with the growth of garden centres selling container grown plants, that peat extraction for horticulture surged. Over 3 million m3 of peat are sold for horticultural applications in the UK every year, with almost one third coming from UK peatlands and 68% imported. In Ireland, extraction vastly exceeds use in horticulture with most exported. The biggest market for peat-based growing media is the amateur gardening sector (72% sales), with the professional sector accounting for a much smaller proportion (26%). While there has been a reduction in the peat content of many mixes, growing sales volumes in the amateur sector negates this overall decline in peat use.

As a substrate for container grown plants, peat has a number of positive attributes – physical or performance related and economic. It has good air porosity, water-holding capacity and nutrient retention. Peatlands are sterile environments and hence little processing is required after extraction, making the production of peat a low-cost process. Peat is a very consistent material and many professional growers have systems in place that depend on this consistency – any change results in a loss of quality and hence income. Nevertheless, there are now well-regarded mixes of peat-free alternatives based on composted bark, green waste compost, wood fibre, loam, coir and/or a range of other materials, often derived from waste products with low intrinsic value. While these might have been considered inconsistent a decade ago, production processes have improved resulting in more predictable mixes although still not as consistent as peat and certainly not as cheap. There is also uncertainty on the environmental footprint of some peat-free alternatives, particularly coir, and costs are rising for other materials as other markets compete for them (e.g. bark and biomass burning).

Why pay more for a peat-free alternative? Peat is a carbon sink but extraction results in carbon release as well as the loss of further carbon sequestration. There are biodiversity and cultural history issues, but another important factor is water management – peatlands have a significant role to play in natural flood management systems which will be increasingly important in the UK as extreme events increase and there is increased development on flood plains. Peat extraction is exploitation of a natural resource: efforts made to restore raised peat bogs are costly but would reflect the real cost of peat if passed on to the consumer.

There is no legislation banning the use of peat as a growing medium but rather an industry-wide voluntary initiative to move away from the unsustainable use of peat. The biggest consumer of peat products is the amateur sector for whom peat-free alternatives are readily available and applicable to most domestic gardens. We can raise awareness of peat-free alternatives, and the reasons for eliminating peat use, in our gardens to inform visitors who might not be aware of the issues or debate (after all, the price tag is often the main driver for sales in the amateur sector). Perhaps an industry-wide initiative to reinvest in peatland restoration would also help to promote the true cost of peat use in horticulture.

By PlantNetwork, January 2020

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