Modern polytunnels can help growers to increase production and improve quality, Maureen Keepin reports.

Polytunnels are often used to provide environment for field-scale protection of fresh producce and to assist early, mid-season and late growing seasons - image: Haygrove Tunnels
Polytunnels are often used to provide environment for field-scale protection of fresh producce and to assist early, mid-season and late growing seasons - image: Haygrove Tunnels

A significant increase in retail nursery sales has led to many growers looking at expanding their polytunnel capacity this year.

The types of structures available include Spanish polytunnels used for field-crop production where the covers are removed after the growing season and then replaced before the next growing period.

Permanent polytunnels range from single bay or multispan up to superbays or split link and they are used to improve the production quality of bedding plants and crops.

Allowing flexibility, a single span can be purchased and then added to as the business grows. Garden centre buildings and structures, which are used as retail outlets, are now forming another part of this market but require stringent building regulations due to public access.

So why are polytunnels so popular? They offer greater control in plant and crop production - earlier or later depending on requirements - because plants are not exposed to the elements.

Ventilation systems are vital to ensure that crops are not scorched and include netted sides, roll-up systems, multispan roof ventilation using rack and pinion systems and fan ventilation, depending on the type and size of structure selected. Pulling air through the polytunnels to control temperature is crucial because it helps to eliminate stagnant air and encourages the creation of stronger and healthier plants.

National Polytunnels marketing manager Kevin Bambury says: "The size of structures has increased significantly and superbays have really taken off."

Providing polytunnel structures to growers and garden centres, most of the company's designs have been developed using Z35 structural steel galvanised inside and out to BS2989. Spans range from single, starting at 5.48m, multispans from 6.55m to 8.08m featuring a hoop to ground tube locking and tensioning system up to superbays in 9.6m spans.

As more and more nurseries now sell on-site they require both growing and retail areas. In this instance it is necessary to meet building regulations because the public have access to the units. These are generally larger bays with heavier box construction and more height allowing better access for larger machinery. Normally a traditional polytunnel door is 2.32m maximum, but here this can be increased to three or four metres.

Bambury adds: "Today we find many growers offer a retail outlet not just for edible crops and plants but also pots and ancillary products. To some extent they are replicating garden centres."

When polytunnels are sited on more exposed sites, screening is advisable to help protect them and extend the life of the polythene. Older models did suffer in winter snow but more modern designs fare well. Improved design now takes snow load into account and this together with crop bars helps to make them a much stronger construction.

Clovis Lande managing director Greg Revell reports: "In Scotland, a 20-year-old structure did suffer damage but the new section was not affected. This has led to an increase in our tunnel sales because growers are prepared to invest more to securely protect their crops."

First Tunnels is introducing a new sliding door option to its range. Sales and marketing manager Gail Burn says: "These doors have been added because they save considerably on space. A single door can be fitted to our 2.44m tunnel and double commercial doors are available for the larger models."

Coming out of its busiest period from January to the end of April, the company reports a reduction in prices, passing on to customers some of the benefits of an exceptional trading year. All its units are single-bay permanent polytunnels with the smallest at 1.82m wide costing £240 including VAT up to a 9.14m by 27.43m polytunnel, which costs around £3,000 including VAT.

Burn comments: "A really exciting development is that we are now selling polytunnels to schools that are including plant growing in their curriculum. This then encourages children to cook and eat the produce."

NP Structures reports sales this year well ahead of budget as growers now have money to invest in expansion. By far the most popular polytunnel year-on-year is the company's 8m multispan, with prices starting from £16 per square metre.

At Polybuild, sales manager Jonty Swales says: "Sales of our larger multispans, which cover around half to an acre of ground, have certainly seen an increase. These have higher eaves to allow improved airflow and are often used by salad growers. One of the chief benefits over glasshouses is that you can achieve greater control by using different polythenes to match the crop in which you are specialising."


Spanish and French tunnels both provide a good environment for the field-scale protection of fresh produce including soft fruits and to assist the early, mid-season and late growing seasons.

The polythene used on these structures is usually removed in the winter and put back in the spring season. Tunnels can be moved from field to field because they do not involve permanent fixtures and Haygrove Tunnels provides a range of polytunnels to protect high-value crops from increasingly unreliable weather.

The tunnels are supplied in variable bay widths, ranging from 5m to 9m. An in-house design team develops new features and this year sees the introduction of electric doors.

Haygrove sales and marketing administrator Iwona Krystyan comments: "This saves considerably on both time and labour because the grower simply has to press a button and 20 doors or more can be opened at the same time in the morning and closed again in the evening."

The polytunnels have a galvanised steel structure that is covered with polythene. Since they are lower-cost, these polytunnels are reported to pay back outlay in fewer than three seasons with most crops.


The first of its type in the UK is a Netafim structure covered in polyethylene that has been supplied to Ornamental Plants of Tarleton, which grows a range of bedding plants.

Eden managing director Julian Gruzelier, who has managed this new-build project and acts as Netafim's technical partner in the UK, points out: "This structure is very different from anything else in the country and as a result vegetable and soft fruit growers are showing considerable interest.

"It is a commercial type of permanent structure covered in polythene rather than glass. We call it a greenhouse but it is so sizeable that you can drive a large tractor through the middle of it and vegetable growers are looking at covering their fields with a single structure.

"This type of building certainly has a role in the marketplace because although it is more expensive than traditional polytunnels it works out at around half the cost of a new glasshouse."

Offering a completely different configuration, the structure is 2x4-inch box section steel and the benefits over a polytunnel include increased load-bearing capacity. Significantly improving climate control, this structure boasts good automated ventilation that includes the roof, because this is where much of the heat sits.

Based in Israel, Netafim has more than 15 years' experience designing and supplying these structures to commercial growers around the world. Their popularity is due to the fact that they offer increased growing density per square metre.

The building just completed was supplied by LS Systems and is 4.75m high to the gutters, giving a huge volume of air, and each bay is 9.6m wide with the total structure offering 1.3ha of growing space.


As the garden centre market continues to grow, companies that produce polytunnels are now extending their ranges into garden centre buildings.

NP Structures is setting up a dedicated team comprising team leader, architect and structural engineer. Sales manager Matthew Harrison explains: "This will allow us to work more closely with garden centres that usually want insulated buildings for retail space as well as outdoor sales areas for plants and other products."

A project that the company has just completed in Bristol is a 30x30m combination of open sales area and heated indoor facility for Kemps Garden Centre. The company is also in the middle of a similar project at Fyfe in Scotland for James Field, where they are providing 30x40m of space.

Fordingbridge focuses on the garden centre market and last year was involved with the Garden Centre Group in reconstruction projects at a large number of its sites. Steve Budd, who works in technical sales, says: "Despite the recession, or because of it, the garden centre market has really flourished.

"Plants are now often under cover outdoors with timber walkways between areas to protect customers from the elements."

Many structures are open-sided. Budd continues: "A major change that we have noticed is in garden centre layouts. These are now designed to take customers around the external displays then lead them into indoor retail space before drawing them through to the till areas."

Polybuild sales manager Jonty Swales adds: "Timber and steel-canopied walkways are increasing because they help direct people around centres. We manufacture our own multispan timber structures because this gives us better control over issues such as delivery and they can be covered in flame-retardant materials, steel or woven materials with insulation."


- Use - what are you going to use the polytunnel structure for and will the public have access?

- Stock - what exactly will you be growing?

- Project budget - you should take into consideration the expected lifespan of the structure to determine cost-effectiveness.

- Build quality - different guarantees are offered. Prop supports to every hoop will help the structure to withstand really heavy snow. Ensure that suitably-sized posts are fitted for the height of the structure.

- Unit location - exposed sites will require extra bracing and protection.

- Adequate ventilation - this is needed to avoid heat inside the tunnel burning stock.

- Topography - request a site visit by the supplier to determine what is best suited to your conditions.

- Planning permission - it is advisable to speak to local planning authorities because regulations vary across the land, with some very stringent.

- Quote - should be in writing and go through all options in detail.

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