Every year, the share of peat used by professional growers decreases slightly in line with long-term Government and industry goals. But last year’s limited peat availability appears to have nudged the process along, according to Catherine Dawson, technical director of wood- and bark-derived media supplier Melcourt and a member of the industry’s Growing Media Association (GMA).
"It made some growers open to new things and we have since hung onto them as customers," she says. The situation has an irony to it, she points out. "One of the criticisms thrown at alternative media is that if everyone used them, there wouldn’t be enough. But we are in no danger of running out — it was peat that came closest to the wire last year."
Yet bark and wood remain one of the few viable alternatives to peat that are available in quantity at the right price, says Dawson. "Even after 25 years of this debate, it still just comes down to that or coir — very few others have emerged."
Melcourt extended its Sylvamix range last year with a Seed & Cutting product — traditionally seen as one of the more technically challenging areas for peat substitution. Together with the Sylvamix Hanging Basket mix, it claimed the best new professional product award at last autumn’s Four Oaks Trade Show.
"A herb grower just phoned to say how impressed he was with the even germination he was getting," says Dawson. But she admits: "Blocking still requires a fine yet firm structure. You can use an adhesive [with a peat alternative] but it becomes too expensive."
On the wider peat argument, she adds: "We sell our products on their technical merit. We don’t denigrate peat — it has been demonised while everything else is seen as benign." For this reason, she welcomes a methodology for objectively measuring the sustainability of different growing media against a series of criteria, soon to be published by ADAS at the GMA’s behest.
"It will yield a score based on transport, water and energy use, and social factors as well as biodiversity," she explains. "Each supplier’s product will fare differently. We only screen our raw materials, but some hammer-mill or extrude, which will score higher. It will better address sceptics’ arguments."
Melcourt is not alone in promoting wood- and bark-based media, as major peat suppliers have also strived in recent years to develop alternatives, generally as an additive in "peat-reduced" mixes.
Northern Ireland-based Bulrush now offers its Forest Gold Plus wood-based medium in its commercial mixes. Professional products director James Hayes says: "Growers are being driven down the non-peat route by their customers. We need to protect our business and coir for us neither practical nor cost-effective."
While cost is one factor attracting growers, "Forest Gold Plus also has very useful characteristics, such as its water-holding capacity," adds Hayes. "Coir may or may not be a long-term solution, but we are trialling a number of new Forest Gold Plus-based blends that we hope will compete with it."
The only exception so far is seeding and propagation, which require small cells to which alternative media are less physically suited, he explains. "Any alternative medium has to meet the mechanical handling requirements as we find them." For that reason, he says: "One-hundred per cent Forest Gold Plus isn’t really a practical proposition."
As to peat, Hayes adds: "The harvest last year was very good and we have substantial reserves built up, which we will protect because we don’t know what this summer will be like. We haven’t backtracked on peat reduction at all. It’s still something we are committed to long-term."
Meanwhile, William Sinclair Horticulture has a new dedicated plant in Cheshire producing its SuperFyba medium from woody garden waste and has said it expects to progressively increase production volumes. But a company representative says: "SuperFyba is not yet being used in our professional growing media, only our retail products. However, a lot of trials of SuperFyba mixes are ongoing."
Wood-based products aside, there has so far been scepticism among growers to the idea of using media derived from other green waste such as food leftovers and gardening waste. Crop consultant Mike Daly aims to change these perceptions with two revised industry guides that he has prepared for the Government’s waste-reduction agency, WRAP.
The two guides — one aimed at composters and the other at growers — will be published later this year, having last been issued in 2011. Daly says he dislikes the term "green waste" for the end product. "According to the Environment Agency, it’s no longer waste," he points out.
"There is a lot of testing and stringent standards with horticultural green compost, and there are various advantages. Some growers see a benefit in their crops due the slow release of nutrients, which are at slightly higher levels than peat-based media — and being denser, it makes pots more stable on a nursery, though it is heavier to handle."
Daly admits: "For seed mixes, your ration of green compost would have to go quite low — five-to-10 per cent, given the nutrient strength. You also need a particle size of 0-6mm — the standard 10mm would be too big for the cell — so you have an extra screening cost." But he adds: "In nursery stock, there are already growers using it at between 20 and 40 per cent."
Trials boost enriched biochar range
Carbon Gold’s enriched biochar range has been shown to increase root growth, reduce watering requirements and suppress nematodes, resulting in stronger, healthier plants and increased yields, according to trials.
Growers working with a variety of soils also found that Carbon Gold peat-free compost mixes enriched with GroChar Soil Improver (90 per cent biochar), performed as well as, and in some cases better than, peat.
Wight Salads head of agronomy Paul Howlett says: "Where we have incorporated Carbon Gold Soil Improver in the very sandy soil at our Portuguese nursery we have seen a 10 per cent yield increase and a lower level of nematode infestation compared with untreated areas."
In addition, Martin Kyte, a product development specialist at vegetable seed breeder Rijk Zwaan, points out: "After trying several other non-peat alternatives for propagating plants, I have found Carbon Gold to be reliable, easy to handle, uses less water, is easy to wet up if it becomes too dry and kind on the environment, as well as producing top-quality organic vegetable plants across our range."
Daylesford Organic Farm market gardener Jez Taylor says: "I’ve been using Carbon Gold as our main compost for two years now and it continues to give high performance with low watering requirements, good germination and excellent plant health."