Increasing demand for new glass and polythene

One of the biggest greenhouse construction projects in recent years is currently underway near Spalding, with 30 ha expansion being undertaken by ornamentals grower Bridge Farm Group, parent company of Neame Lea and Zyon. But is this confidence in the sector mirrored elsewhere, and what trends are developers seeing? Richard Crowhurst reports.

“Today’s new glasshouses tend to be much higher than of five years ago,” comments Tony Walker, Managing Director, Ebtech Glasshouse Systems Ltd. “This is to provide growers with greater control of the environment around the crop. For example, most salad crop nurseries are now being urged to build from five or six meters upwards. In general terms the demand for new structures over the last couple of years has increased, with a number of new glasshouses being built next to facilities which can supply them with waste heat.”

This demand for additional height is also being seen in polytunnels, although not to the same degree. “Many of our polytunnel enquiries are for higher structures,” agrees Nigel Carr of Northern Polytunnels. “Our standard height to the underside of the gutters used to be 2.2m but we are increasing supplying polytunnels which are 2.5m and 2.7m to the gutters. We have also seen an increase in the size of the enquiries, with a significant number of projects between ½ acre and 5 acres.”

Both Nigel and Tony say that it is the expansion of existing businesses, rather than new entrants, which continues to invest in new glass (or plastic), but that demand is coming from across the protected cropping sector. “Most of our larger enquiries are for business expansion plans, and new entrants are almost unheard of,” continues Nigel. “We’ve seen investment across a range of sectors.  Heated polytunnels for soft fruit production to extend picking dates from March through to December is particularly notable, and by working closely with growers we’ve been able to develop a cost-effective structure which allows just this.  Ornamental horticulture is also seeing some ambitious expansion plans, with a number of larger growers also increasing their protected area.”

“There seems to be a greater interest in, and demand for, medicinal cannabis and glasshouses are being built with this in mind, or old glasshouses are being adapted,” adds Tony. “Demand for new developments is also coming on the back of those Renewable Heat Incentives (RHI) which are still in place, for example for projects which include ground source heat pumps and CHP. There is a lot of interest from soft fruit and tomato growers in new buildings as it offers them better control of their growing environment.”

While VDH Foliekassen have been supplying film-covered greenhouses for more than 25 years, they are relatively new to building in the UK, constructing their first greenhouse in the country last year. “My perception is that expansion by existing growers is driving investment in new structures,” comments Ben van der Heide. “But as said we are not that experienced in the UK market. Much of our demand is coming from the soft fruit sector and we are about to start building a 2 ha project in Scotland this April. We are also seeing interest from ornamentals producers.”

As the understanding of Next Generation Growing has increased, and growers increasingly move to semi-closed production systems, the need for sufficient air volume in the greenhouse becomes even more important – a key driver for the higher specifications that companies are being asked for. “In general is important a huge air volume, so the greenhouse must be built high enough to create a large air buffer, and there needs to be good ventilation and climate control,” adds Ben.

“Large structures require good ventilation,” agrees Nigel. “The development of fully automated roll-up sides, along with polytunnel roof extraction fans has allowed Northern Polytunnels to remove the human element from temperature control, thus removing labour costs and creating a harmonised environment.”

Increasing levels of automation – both in terms of climate control and operations – are something that greenhouse designers need to be aware of. Reports suggest that Bridge Farm’s new glass at Spalding will include a range of automated handling systems, with Chief Executive David Ball saying, “The new facility will feature a range of state-of-the-art machinery and automation, and will also safeguard the jobs of hundreds of staff in and around Spalding. Our new site represents another key milestone in the evolution and expansion of Bridge Farm Group.”

The demand for both glass and polythene structures remains buoyant and Nigel Carr points out that, “Some growers will always want glass-clad greenhouses whereas others will opt for polythene.”  He adds that the decision between the two is usually driven by a number of different factors, including crop requirements; production methods; available capital and the grower’s preferences. “Maintenance costs, construction timescales, ground preparation, heating costs and many other factors will also influence decision makers,” he continues. “Over recent years we have focused on offering growing solutions which were previously unavailable with polytunnels, thus further closing the technological gap between glass and polythene.”

These include features such as UV-open temperature-regulating films and options for fully-automated ventilation. With polytunnels able to offer the same efficient rain water collection and accurate irrigation systems that you would find in glass structures but costing around £25 per square meter including construction, Nigel feels that, “It is understandable why many large scale producers are moving towards polytunnels. We have recently undertaken a number of multi-span polytunnel projects, including two hectares in Angus, 1.5 hectares in Fife, and a number of smaller structures across the country.”

Light transmission is another key factor in choosing between glass or polythene and Ben observes that, “Vegetable growers mainly build glass, while ornamentals, tree nurseries and soft fruit are more open to using films because of the different film properties available such as diffusion and UV-openness.”

“Light is a primary growth factor for all plants, therefore a lot of features in greenhouses are based around maximising light levels, and spreading it as much as possible,” agrees Tony Walker. “For example deeper glazing bars and frameless vents are available to reduce the shade and maximise the light input. One alternative to glass is F Clean film. This is a material which looks like plastic film, but behaves like a membrane, meaning it has to be tensioned. It is available in clear and diffuse versions and can be installed in both a single and a double layer, and is already being used on many cabriolet houses.”

When it comes to glass he points out that diffused glass is now available in a range of varying haze grades to spread the direct light equally amongst the crop. “Other features to help give better light levels in the crop include having the steelwork white powder coated,” he adds. The open-trellis style Twinlight posts from BOM greenhouses enable better light distribution through the glasshouse, while using less steel in the structure, and they were used to construct a new greenhouse for Valley Grown Salads a few years ago.

Despite the development of new features such as these, new glasshouses represent a considerable capital investment and Tony says that, “The demand for used glasshouses is still very popular as many of the UK growers still like their traditional 6.4m spans and low post heights. As many Dutch supplied glasshouses are much wider and taller, especially for salad crops, in many cases these can only really be supplied as used units. The ability to be able to attach the extension to existing structures is another reason why used glass is still popular, and then there is the cost savings compared to new units.”