Polytunnels: Second generation

As more permanent structures gain acceptance, growers are utilising new developments from air treatment to automation, Gavin McEwan reports.

Polytunnels: adviser maintains that development of structures can make planning approval less problematic
Polytunnels: adviser maintains that development of structures can make planning approval less problematic

Horticultural polytunnels are evolving into permanent, highly designed, capital-intensive structures with arguably as much in common with glasshouses as with their flimsy temporary forebears. This sounds as though it should present growers with a greater problems in gaining permission for them, but according to one seasoned adviser to the industry, the reverse is the case.

"We are now into the second generation of polytunnels, which are no longer temporary structures moved around a farm," says Tony Aspbury, director of development consultancy Antony Aspbury Associates. "For us, there continues to be successor schemes to original proposals."

These are taking the form of year-round structures that may include heating and even CO2 enrichment, he adds. "It’s the direction of travel that most growers are on and my landscaping colleagues say it makes it easier to gain approval for than mobile, temporary structures, simply because it’s easier to present a case for something when you know where it’s going to be."

Overall, he says: "We have already won the battle on principle — there is widespread acceptance that they have transformed soft-fruit growing and led to import substitution. We find the planning authorities very good, certainly the officers. The elected members can be susceptible to local pressure.

"We have had a variety of experiences. It depends on the region and the community you are dealing with. In the Wye Valley area of outstanding natural beauty we have dealt with around 15 applications for tunnels and have had one or two cases of quite determined local residents’ groups opposing them."

Community relations

As a result, Aspbury says: "One large grower we work with has turned around its community relations. But it’s an area where some growers are more astute than others. We ourselves have done a number of pre-application engagements with communities on behalf of growers as part of the process of gaining planning permission.

"These don’t change the hearts and minds of the people who are adamantly opposed, but where people are more relaxed it’s a good way of tapping into that. Sadly, nothing divides a rural community like polytunnels. Older people tend to see it as a necessary part of the rural economy — they recognise their important role in bringing jobs to agricultural areas. But incomers often have an image of what the countryside should look like. Then there are other issues involved such as migrant labour, which given the political context can cloud the issue."

He continues: "The idea that they cause a problem with water run-off used to be a popular myth, though it’s less heard now. We still submit a flood-risk assessment and explanation of how the water will be used and recycled, though many growers don’t recycle because of the risk of disease transfer. Similarly, transport is not a big issue because it’s unlikely to be greater than for other forms of modern agriculture."

Direction of travel

Meanwhile, this "direction of travel" in the structures themselves is increasingly blurring the boundary between polytunnel and glasshouse technology, says Northern Polytunnels commercial director Nigel Carr.

"The problem growers have had with polytunnels, both for food production and plant propagation, is high humidity and the disease risk this brings. That’s why tomato and cucumber growers have stuck to glasshouses — they can vent easily," he points out.

A solution is the Eco Climate Converter from Israeli supplier Agam that Northern Polytunnels has begun supplying. This draws moisture out of the air, together with any fungal spores, while returning the heat from the water to the growing environment, Carr explains.

It achieves this by passing the moist air through a "shower" of lithium chloride, a powerful desiccant. This is then heated to evaporate the water and recycle the desiccant, while the water is then recondensed via a heat exchanger and the heat that is liberated from this is then returned to the growing environment.

Each unit will treat air within a 1,000-2,000sq m area, with a higher density required for crops such as tomatoes with a high total leaf area. The company says it guarantees savings on heating of 40-70 per cent, with a resulting return on investment of three years or fewer. "We have four in a Midlands nursery, which is already seeing savings of £4,000 a month on their bills," says Carr.

In tandem with this is a trend for more finesse in the structures themselves, he adds. "Until now, polytunnels have not been calculated structures. Ours were known to be strong and able to withstand high wind and snow load. But now we are developing structures created with glasshouse design software so the load on the square posts and trellises is calculated."

The resulting highly efficient design "looks like a glasshouse but with polytunnel hoops overhead". This also makes polythene a viable alternative to glass for year-round production "especially as you can now incorporate diffuse or ultraviolet-open films", he says.

Sophisticated films

The films themselves continue to increase in sophistication and Devon’s XL Horticulture has recently launched two new variants. DuraTherm is described as a four-season film with the same physical characteristics as its established diffuse and UV-open DuraLight, but with around 83 per cent thermicity, a measure of the transmission of infrared light, for greater heat retention.

For low-temperature crops such as blueberries and cherries, which are increasingly grown in a protected environment, XL’s DuraCool is an adaptation of a product manufactured for the African market that has the opposite aim of keeping heat out. "To do this it uses a microfine aluminium diffusion additive that is far more efficient than any other on the market," says director Les Lane. "The development took 10 years of research, trialling many different diffuser additives."

Both films boast an ISO 9001 specification and certification sheet, he adds. "One of the things that ticks me off is the claims people make about films. So people think that, for instance, a thicker film is a stronger film. But can they back that up with a data sheet? No, they can’t.
"XL Horticulture can issue a spec/data sheet for all of its covers, all from an ISO-registered laboratory, as well as a spectral transmission graph. That’s why we are probably the most technical supplier of films in the market. If we say our films are stronger it’s because we have tested the competitors’ films — in the laboratory — and machines don’t lie and are not subjective."

Haygrove earns industry recognition

Last November, the Worshipful Company of Fruiterers presented Haygrove growing systems managing director John Berry (pictured, right) with its management award, showing how widely appreciated the Herefordshire company’s contribution has been to the soft-fruit industry.

Berry has been at Haygrove for 14 years, seeing it rise from a purely local supplier to selling 75 per cent of its tunnels overseas, a presence in around 50 countries and five staff in research and development.

"We transfer glasshouse technology to the field scale at a cost that allows a two- to three-year payback," he tells Grower. "You can build and equip a modern polytunnel for around £10 a square metre, compared with around £30-40/sq m for glass."

Initially the challenge was simply to make bigger structures, he adds. "The next phase was to make them as modular as possible and to incorporate water harvesting, electric roller ends and even roof venting. Now we are looking at automation, allowing you to control it all from your iPad. But we also see substrates as an important technical challenge," says Berry.

Being growers as well, with 180ha across five sites growing all the berries plus cherries, allows Haygrove to test new developments on a commercial scale first, he explains, with annual open days to demonstrate them in practice.

"The area used to grow soft fruit in this country is pretty much the same as 15 years ago, perhaps even slightly smaller," he points out. "Tunnels are the main, but not the only, reason why that area is now so much more productive."

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