Reducing the level of peat for crop production and plant propagation is proving difficult for all but fruit growers, who are increasingly using coir with some success. Green and vegetable waste compost generally is proving a variable replacement for a proportion of the peat used in substrates. Yet there is a glimmer of hope that it at least can be made more suitable for use by growers.
Institute of Food Research professor Keith Waldren has developed a patented process that controls the degradation of plant material. Unlike normal composting, the material he has produced retains significant structure to make it a high-quality growing medium suitable for replacing peat, he claims.
"With industrial composting the raw material is broken down mostly into a pile of bacteria and there's very little structural material left," says Waldren, whose HortLINK project was funded by Defra and used leafy vegetable, fruit and cereal by-product waste.
"Another big problem (with conventionally produced compost) is that it lacks uniformity because its raw material comes from different sources and is made by different processes and there's also the issue to traceability."
Advantages of coir
ADAS consultant Chris Creed reckons that virtually all soft fruit growers have moved away from peat into coir. This is for environmental reasons and because coir is very suitable and has a number of advantages over peat.
"Nursery stock growers have stayed on the peat route and I don't think the Dutch will ever stop using it," he says. "Not many growers are using green waste compost and I don't foresee much being used in its present form. Its main problem is variability - every load seems different and all sorts of things go into it. One of my nursery stock people used some and half of it was polythene. You can use it but it's difficult to manage and it can have shockingly high levels of conductivity."
Propagators such as Hargreaves Plants are moving away from peat into coir. Commercial director James Petchell says coir is better drained, has higher air-filled porosity and poses much less risk of carrying soil-borne diseases.
Hargreaves use a range of modules and containers for propagation. For example, strawberry plants are raised in 60-cell and 40-cell trays, blackberries in 9cm pots and blueberries in 9cm and two-litre pots. However, about 60 per cent of its strawberry and raspberry propagation is still done in the field. In the past three to five years there has been quite a big move of its propagation into substrate but this trend has probably levelled off, Petchell reports.
"Some soft fruit propagators are now beginning to move back into the field where virgin (disease-free) sites are available," he adds. "This is better in a way because it's cheaper and you're less likely to overdo the watering."
The company has a 4ha new variety trial site where in the past the plants were grown in the soil. But because it aims to use the site in the longer term, it is now growing strawberries on tabletops and raspberries and blackberries in pots, all in coir.
Although the Vital Earth composting company uses mostly the same raw material as others, mainly green waste, it claims to produce a higher-quality material suitable for plant propagation. But because the material is too nutrient-rich on its own, it is mixed with 25 per cent composted bark.
The company's research and development manager Dr Arnie Rainbow believes that its compost is superior because it is produced by an in-vessel process under cover. Unlike a lot of compost that is produced outdoors and turned by tractor fore-end loaders, it is not contaminated by wind-blown weed seed or drenched by rain.
"We are able to control our compost's bulk density and moisture content and produce material of uniform quality," he asserts. "During processing we blow a lot of air through it to keep it aerobic and help keep beneficial fungi and bacteria healthy."
Vital Earth composts 80,000 tonnes of green waste a year collected from surrounding counties. It is sold mainly to growers and garden centres for raising a range of subjects including fruit trees and nursery stock. For containerised nursery stock it has the advantage of discouraging the growth of liverwort.
"It's not easy for green waste compost to replace peat or coir for propagating soft fruit in small cell trays," Rainbow admits, "but it's okay for larger containers."
Green waste learning curve
Consultant Susie Holmes reckons that the industry is still early on in the learning curve in its use of green waste compost. And she believes that most composters are unwilling to invest in the right production facilities to make a high enough quality of compost for growing and propagation.
"There are growers trying to use compost (made from green waste) but it's no good on its own," she affirms. "It's too heavy and its nutrient content is too high, so it has to be blended with something to get the right nutrient level and structure."
The Horticultural Development Company's response to Defra's recent consultation on the continued reduction of peat use by growers makes it clear that the industry has already achieved a good deal. It is estimated that 30 per cent of the total growing medium used is now peat-free - a 19 per cent rise since 2007. Coir in particular has proved a suitable and often better alternative.
After trying a number of different substrate mixtures, the Hall Hunter Partnership settled for 100 per cent coir for a proportion of its fruiting strawberries and raspberries on a three-year cycle. As propagation requires a heavier substrate for rapid root growth, a 50:50 coir/peat mix has proved the best answer.
One of the company's managers, Andrew Zygora, says that last year 10 per cent of its strawberries were grown in coir bags on tabletops and next year the proportion will be around 35 per cent. Currently the price of 24-litre coir growbags is lower than that for peat - generally £1-£1.20 each.
Coir lends itself well as a soilless growing medium. Unlike peat, its pH is naturally more or less perfect at 5 to 6.5 compared with around only 3.6 for Baltic peat, which means its pH has to be adjusted for berry crops apart from blueberries.
Another advantage of coir bags is that they do not need fluffing up before use because the medium retains its original good consistency and shape. In addition, it is easier to plant into, does not slump with first, second or even third use and is less prone to waterlogging than peat because it is freer draining.
Coir's main potential disadvantage is that supplies are finite and as peat use is phased out and demand increases, the material may run short. But suppliers of the product point out that coconuts, from which it is made, are widely grown throughout the tropics year-round. Furthermore, so far only a relatively small proportion of the husks produced by the crop are currently processed into coir.
The largest proportion of young plants for growing on come from Holland but there are numerous UK propagators able to supply growers, particularly those producing berry fruit, who require new varieties. Meiosis, for example, which handles East Malling Research-bred material, has seven newly released strawberry varieties on its books.
Plants of these are produced by Berryplants, Darby Plants, Hargreaves Plants, TJ Moore, RW Walpole & Partners, Welsh Fruit Stocks, Edward Vinson and Woods Nurseries Plants. Most of their plants are field-grown but like Hargreaves they also produce tray, cell and potted plants invariably in coir or coir/peat mixtures.
Coir finds favour among soft fruit growers
Soft fruit growers are switching to coir both from peat and from soil-based growing, according to Botanicoir director Kalum Balasuriya.
"We have expanded significantly in soft fruit and, working with large growers, we have made a specific blend for soft fruit, with very high AFP (air filled porosity) to ensure free drainage."
Indeed, its recent success in winning orders has put a strain on the family-run company, he adds. "We were slightly overwhelmed this year. But we have expanded our factory in Sri Lanka to cope."
However, he says the potential to expand production further is considerable. "Around 2.9 billion coconuts a year are harvested in Sri Lanka and only 35 per cent of the husks are put to use. Also, coconut tree planting is expanding in the north of the country, now that the conflict there has ended, which is all good news for us."
With an international market comes complications in the terminology, he adds. "In Holland and Australia they call it 'cocopeat', also 'coco coir' or 'coir peat'. It can cause confusion."