Professional growing media

Growers can benefit from using the latest sustainable and responsibly sourced growing media but there are issues to consider for novice users, Sally Drury explains.

Growing media: more growers want to be part of trend toward sustainable material - image: HW
Growing media: more growers want to be part of trend toward sustainable material - image: HW

Can it really be more than a quarter of a century since Horticulture Week reported that the "peat war" was hotting up as conservationists took growing-media producers to task? Certainly back in the late 1980s and early 1990s newspaper headlines were screaming: "For peat's sake save the bogs," as it was announced that 96 per cent of the raised bogs in Lancashire, Somerset, East Anglia, South Yorkshire and Scotland had been lost to agriculture and building since 1850, but with "horticulture being the main villain since World War Two".

In 1990 environmental groups including Friends of the Earth, the Royal Society for Nature Conservation, Plant Life and the RSPB joined forces against peat extraction. The Department of Trade & Industry was called on to revoke planning permission for peat extraction, Ebbw Vale Garden Festival threatened to exclude plants grown in peat and Severn Trent Water plus two local authorities declared themselves peat-free zones.

In Horticulture Week we wrote: "Horticulture can't afford to turn a blind eye to the growing-media maelstrom because the anti-peat campaign may do for growers and landscapers what Edwina (Currie) and eggs did for farmers."

Peat-use targets

Over the years Government targets to reduce and eliminate the use of peat have come and gone. Former minister of state for the environment Michael Meacher threatened compulsory measures, which were then squashed by EU trade laws. By 2015 all councils were to be peat free. It did not happen. So what has happened and has anything good come out of the last 25 or 30 years of discussions, campaigning and missed targets?

The answer is definitely yes. Following research, development and trials, we now have a much broader choice of growing media than ever before and, more importantly, the industry's knowledge and expertise has grown and strengthened.

"The best thing for ourselves coming from the massive amount of development and trials work is the knowledge gained about the individual materials," explains Petersfield Growing Mediums sales manager Neil Williams. "This has led to valuable improvements in all mixes including peat-based, reduced-peat and specialist mixes such as roof garden soils."

Petersfield, based in Cosby near Leicester, continues to find improvements in the growing media, occasionally gleaning ideas or inspiration from colleagues in sister company Hewitt Sportsturf, and vice versa. Working with some of its key customers, Petersfield has honed mixes to produce plants that consistently win medals at events such as RHS Chelsea Flower Show.

From the start 30 years ago Melcourt Industries, based at Tetbury in Gloucestershire, has been at the forefront of the development of sustainable, responsibly sourced growing media. Continuing to grow and invest, the company has just put in a planning application for a further extension to its production site to meet demand. Technical director Catherine Dawson finds an increasing number of growers who want to be part of this trend and says plant retailers are also keen for more product to be peat-free.

"Conversations with high-volume purchasers of plants for retail also suggest that responsibly sourced growing media are working their way up the corporate social responsibility agendas of more and more buyers," she comments.

Melcourt is proud that many of the gold medal winners at Chelsea are users of the company's Sylvamix medium. "Surely this indicates to the greatest sceptics that quality is not dependent on the use of peat," adds Dawson.

The choice of peat alternatives grew again last year as ICL entered the professional peat-free growing-media market with the launch of Levington Advance Sustain. Boultons is one nursery already using it to produce quality plants. But when switching part or all of your production from peat-based to peat-free, growers need to consider various management issues.

"Growers making the move to any peat-free mix need to adapt their current practices and growing systems - particularly watering/irrigation regimes and nutrition programmes," says ICL technical area sales manager for the North West Dean Sandford.

Greater vigilance

The physical properties of peat-based growing media differ widely to non-peat alternatives. Commonly, peat-free mixes will contain coir, bark and wood fibre. As such they are more freely draining, so greater vigilance is required when it comes to watering and "little and often" is usually the best approach.

"Peat-free growing media can give the appearance of being dry on the surface while remaining moist below," Sandford points out. "Failure to observe this can lead to overwatering, which in turn causes nutrient deficiencies due to leaching and fungal pathogens."

Growers should also be aware that peat-free growing media mixes tend to have higher pH and EC levels, as well as higher rates of degradability. These can be addressed and compensated for by changes in the levels and composition of the base fertiliser.

"Products such as our ICL Start & Gro base fertiliser, with additional calcium nitrate, can balance the degradability and nitrogen draw-down issues often associated with peat-free growing media, especially where the higher proportion of fine barks are used. This issue can be further managed with routine maintenance fertilisation," Sandford advises.

Of course, high pH can lead to iron and magnesium deficiency so growers also need to give careful consideration to the source and longevity of added micronutrients. ICL's Micromax Premium contains high levels of both Fe and Mg in fine granular form and has longevity of up to 16 months. Growers should also be aware of two new ICL products.

"New this year, two controlled-release products - Osmocote CalMag and Osmocote Iron - both have threeto four-month release patterns," says Sandford. "Utilising advanced coating technology, these products are mixed into the substrate and can be used alongside other Osmocote products or with water-soluble programmes."

Osmocote CalMag delivers nitrogen, calcium and magnesium on a daily basis. "Some crops such as blue conifers, magnolias and hydrangeas are particularly magnesium-demanding while others, such as Rosa, Buxus and Taxus, are calcium-demanding. CalMag is also ideally suited to pot plant production in soft-water locations," says Sandford.

Osmocote Iron is a fully coated fertiliser releasing iron on a daily basis. It is said to be ideal for use in peat-free growing media, particularly for iron-demanding crops such as primulas and vincas, generating better leaf colour and helping to optimise photosynthesis.

Water assessment

When using peat-free growing media it is particularly important to assess water quality/type. Hard water will in time lead to increased pH levels and compound other issues. Conversely, soft-water types need to be adjusted to ensure there is sufficient calcium and magnesium available for both vegetative and generative/final growth phases. According to Sandford, this is particularly so when there are high proportions of coir in the mix.

It may sound complex, perhaps even a little daunting, if you have been reluctant to take the plunge and go peat-free. But suppliers now have the knowledge and experience to assist. Sandford says: "Our ICL Peters and Universol water-soluble fertiliser (WSF) ranges, when combined with our decision-support tool AngelaWeb, can take into account your water quality, base nutrition level, controlled-release fertiliser and WSF inputs to arrive at a complete nutrition solution for more than 900 crops."

Over the past 25 years most growers have trialled peat-free mixes in their production. Some have opted for peat-reduced while others have gone totally peat-free. Melcourt reports that Rugby-based Bernhard's Nurseries, grower of more than one million trees, shrubs, roses and conifers annually, has switched to 100 per cent peat-free compost in all its own production.

"The group has used peat-reduced media for a number of years, as well as Melcourt Potting Bark to 'top' pots, reducing labour and herbicide usage," explains Melcourt technical director Catherine Dawson. "However, Bernhard's has also been trialling production in Melcourt Sylvamix alongside existing products for the past two years."

Bernhard's general manager John Marsden confirms: "We have been so impressed with Sylvamix that we have now made the full switch to 100 per cent peat-free media across all the group's own production, and customers seem pleased that we are making this change."

Melcourt helps growers through any transition to a new growing medium. Technical sales managers Neil Gray and Richard Cave, both former nurserymen, offer advice and guidance. Dawson says: "Many new users are surprised at the ease of the transition and find that there are other advantages when using Sylvamix, such as faster potting rates, less wastage, cleaner tops with less algae, moss and liverwort and an ease of handling that they hadn't previously known was possible."

Premix protection against fungal root diseases

Offering convenience and accuracy, Prestop can now be premixed into growing-media mixes to provide protection against fungal root diseases. A registered biofungicide, Prestop contains the mycelia and spores of a highly aggressive naturally occurring soil fungus Gliocladium catenulatum strain J1446.

Able to survive in the rhizosphere and around the roots for several weeks, and on foliage if applied as a spray, the fungus attacks and suppresses a range of pathogens. It is already popular mixed with substrate and offers tangible benefits.

ICL technical manager Andrew Wilson explains: "Safe for beneficials and compatible with many pesticides, Prestop can be incorporated into IPM programmes. It does not cause plant scorch, there is no worker re-entry interval and no harvest interval."

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