Peat is a substance that the horticultural industry has come to depend on. Nurseries, garden centres, landscapers and hobby gardeners alike, we are addicted to peat.
In this article, Joe Clancy examines the importance of peat, the consequences of its use, the alternatives and the likely-hood of the industry abandoning its favorite growing medium
Peat was first introduced to commercial horticulture in the 1930’s to Europe and was chosen for use in compost mixes because of its light weight and its high water retention properties. Peat's main physical properties are its high air porosity, low bulk density and high water retention qualities (peat is 95% water before being cut). It's air filled porosity attribute is important for good air flow to be present and also to allow good root penetration in the soil. Peat’s fertility level is relatively low requiring the addition of nutrients and is also a sterile source of growing media that inhibits pathogens dangerous to plants. But because of peat’s low level of nutrients and pH it can be amended to suit the growers need with the addition of fertiliser and lime. This gives peat, as a growing medium, a wide range of applications for plants.
Yet, peat is a finite, non-renewable resource taking thousands of years to form. Although its use in horticulture is not solely to blame for dwindling resources (peat reserves have been lost due to natural factors, building, intensive agriculture and also its use as an energy source), the horticultural industry is responsible for consuming twice as much peat used for energy purposes. While there are massive reserves of peat in the Baltic countries, these are unsuitable for industry use because of their immature chemical and physical properties. But extraction continues, as peat is also big business. For example, according to their 2007/2008 annual report, Bord na Mona made a turnover of 371.2 million euro.
The prolific scale and rate of peat extraction has seen many peatlands destroyed. Only 6% of Britain’s original lowland peat bogs remain, of which, only up to 5,000Ha are still in good condition. Low lying raised bogs are a diverse habitat of plants and animals that have adapted to that environment. As mentioned by Professor Valerie Hall, speaking at the Botanical Gardens in Dublin 2008, irreversible damage has been done to most bog land habitats, as invasive alien plant species (Gunnera tinctoria) are now thriving on peat lands where the upper surface of the peat have been cut. According to Flora Hibernica, 92 per cent of bog lands have been destroyed in Ireland and the remaining intact 8 per cent makes up 51 per cent of all bog land remaining in Europe.
Peat extraction was to be banned in the U.K. by 2012, as part of the 1997 Biodiversity Action Plan (this was later abandoned due to the economic downturn), and a number of organisations such as the National Trust and the Royal Horticultural Society (RHS) organized campaigns pushing the public to be 90% peat free by 2010. In fact the RHS bans the use of peat at its flower shows and gardens. Many peat lands are now protected further restricting harvesting and raising the cost of peat, making alternatives more viable. Corporate Social Responsibility programmes on peat reduction, run by many retailers, are now giving customers better choice of peat alternatives.
Various trials, such as the RHS at Wisley have proven comparable results to peat with the use of coir, a peat-free growing medium by-product of coconut husks. Studies on the physical and chemical properties of coir have shown that it has better water retention abilities, higher air porosity and better drainage than peat. Also, amendments to reduced peat products, a product comprised with 50% peat to install confidence in the customer of its capabilities, acted as a stepping stone to peat free products. Possessing much of the same chemical properties as peat, but has less feeding requirements, for example, the addition of lime to raise pH. With additions of loam, levels of drainage qualities and organic matter increase along with the media’s buffering capacity.
There is a severe lack of conclusive evidence comparing peat, peat reduced, and peat alternative products, along with their effects on germination, to each other. Further conclusive testing over a broad range of plant species is needed to address the viability of peat free growing media.
There is a severe lack of conclusive evidence comparing peat, peat reduced, and peat alternative products, along with their effects on germination, to each other. Further conclusive testing over a broad range of plant species is needed to address the viability of peat free growing media.
In my own experience (my thesis was an investigation into the effects on seed germination using peat alternatives), Coir, a by-product of coconut husks, is quite an exceptional growing medium. I observed equal growth in comparison to plant species in full peat growing medium and recorded no incidences of capping, scorching or stunted growth. It has three times the water holding capacity of peat and comes from a cheap, renewable, unwanted waste by-product. Its water retention capabilities alone would allow for huge savings for nurseries dealing with water charges. However, it has poor nutrient retention and is unsustainable due to the fact that it must be imported, mostly from Sri Lanka, attaching a large carbon footprint to its use.
Other alternatives include green compost (grass clipping, leaves, garden waste) and pine bark. Pine bark has been found to be only effective when mixed partially with peat and it tends to make nitrogen unavailable to plants. While green compost tends to increase pH levels and can have varying chemical properties due to fluctuations in its composition's sources. Another player on the scene is wood fibre. Made from wood chips and by-products of the forestry industry, this growing medium has excellent nutrient retention, but is rarely used on its own as a growing medium.
Peat alternatives have come a long way in recent years, with ericaceous peat free compost entering the market, filling the void and answering one of peat free composts strongest criticisms of not being able to sustain acid loving plants (the majority of peat alternatives being alkaline in nature). This growing media uses composted pine needles and bracken.
Peat has long been established as the number one choice of gardeners for growing medium for the better part of a century. With its impressive track record, physical and chemical properties, horticulturalists, amateur gardeners and nursery stock growers are wary to try unproven methods and media. Trials carried out on reduced peat products and peat free products in the past that reported terrible results, compared to peat, furthered scepticism of reduced peat and peat-free growing media.
One thing the peat alternative skeptic should remember: PEAT ALTERNATIVES SHOULD NOT BE TREATED LIKE PEAT!
Poor education and mismanagement are responsible for the majority of bad press on peat alternatives. Trials conducted by the RHS have shown that each peat alternative has a narrow range of plants it can sustain successfully, with some mediums being very plant specific. Each alternative also has quite different feeding requirements, due to varying nutrient retention capabilities (Cation Exchange Capacity Levels). Problems such as unsuitable pH (improper management of composting) and over-watering (easily happens with coir) are usually the fault of the grower, not the growing medium.
With all this in mind, it is clear.....
More research is needed for a new growing medium that is cheap, readily available and as effective as peat. But a leap of faith is needed by many nursery growers in this country. However, many have already taken this step, but more can be done to promote the large scale use of peat alternatives in Ireland. It might be worth taking a note from the RHS and banning the use of peat products at Bloom to bring wider attention to the issue.
.....and for all the nay sayers who don't believe we can break the habit and embrace peat free alternatives, bear this in mind...
.....and for all the nay sayers who don't believe we can break the habit and embrace peat free alternatives, bear this in mind...
.....it took several decades for peat to be accepted as a growing medium by horticulturists in Europe............and look at us now.
Joe Clancy
BSc. Horticulture
HND Landscape Design
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