Taking advantage of the latest structures can help a nursery maintain its reputation, says Sally Drury.

Boningale Nurseries: polytunnels built by Keder Greenhouse
Boningale Nurseries: polytunnels built by Keder Greenhouse

Boningale Nurseries, well known as a leading supplier to the British landscape industry, has a reputation for providing high-quality stock and it is a reputation it means to uphold.

The 40-acre site just outside Albrighton, near Wolverhampton, was originally home to the Bakers nursery, which survived two world wars and was renowned for its production and breeding of delphiniums and Russell lupins.

Mike and Pat Edwards took over the nursery in the 1970s, changed the name to Boningale and developed it to supply a diverse range of home-grown stock to the landscape, amenity and retail sectors.

Today, under the chairmanship of Tim Edwards, Boningale Nurseries produces and contract-grows a huge variety of perennials, grasses, hedging, shrubs and trees, supplemented with specialised stock brought in from trusted UK and European suppliers.

With a client base of landscaping contractors, local authorities, grounds maintenance contractors, landscape architects and designers, construction companies and other nurseries, Boningale supplies more than one million plants annually — the vast majority in containers.

Propagation department

Most of the plants on the nursery begin life in the propagation department, where young plants are raised from seed or cuttings. Once potted, they are likely to be grown-on under the protection of a polytunnel — and Boningale has quite a few.

There are single, multi-span, standard and low constructions from a number of companies including Northern Polytunnels, Fordingbridge and Clovis as well as claddings from XL Horticulture, among others. But two of the newest are structures by Keder Greenhouse and Polybuild.

The Keder multi-span is by far the largest single structure on the site. It is light and airy, and it is expansive. It comprises six bays, giving a total width of 48m, and is 80m in length. To increase ventilation, the two central bays are in cathedral style and are 1m higher than the outer bays, which are the standard 2.5m to the underside of the lower gutters. Electric vents are fitted.

For strength, the frame of the house is manufactured from ZN35 high-tensile structural steel tubing, 44.45mm and 50.8mm in diameter. This is weld repaired with molten zinc and pre-galvanised inside and out for protection against corrosion.

The steel tubing has typical mechanical values of 350N/mm2 minimum yield strength (compared with 220N/mm2 for normal steel) and minimum tensile strength of 450N/mm2 (compared with 300N/mm2). The steel is sourced from UK manufacturers and has complete traceability. Brackets are also manufactured and plated in the UK and are made specifically for Keder.

Looking overhead, it is noticeable that the hoop spacing is closer than in some polyclad houses. Adding to the strength of the structure, hoops are spaced every 2m with cross bracing on every hoop. The gutters are made from pre-galvanised 2mm steel sheeting and are fitted along both sides and in the valleys of the structure. Downpipes at the end ensure that rainwater is harvested and stored in nearby steel tanks.

Wide access doors, hanging on overhead tracks, are positioned at the ends in the middle. These are made from 40x40mm box section steel and hot-dip galvanised. All fixtures and fittings are plated to protect against corrosion and to reduce maintenance. With thoughts of making plant handling more efficient, a central concrete path cuts through the middle of the house. In future a conveyor may be run into the house from the potting barn.

Efficient ventilation

Ventilation is provided by the side walls and, although Keder offers an electric thermostatically controlled system, the Boningale construction works off a manual gearbox and provides an opening of 1.3m. It is simple, efficient, maintenance-free and, thus far, trouble-free. To boost airflow further, central roof vents have been incorporated into the higher third and fourth spans.

When it comes to the cladding, the new house is a hybrid. The roof is Luminance THB AF (Anti-Fog), Visqueen’s plastic film that combines thermic and light transmission properties (87 per cent) with high diffusion characteristics (in excess of 90 per cent) to help control temperature and reduce infrared radiation. It is guaranteed for five seasons. The sides and ends are Bubble Keder Polydress, a nine-layer laminate plastic system developed to make the house safer, lower-maintenance and more cost-effective than traditional glasshouses.

Air bubble sandwich

The plastic forms an air bubble sandwich — a giant version of the bubble wrap — and combines light transparency with good heat insulation. It comes in 2m widths with a welded seal, making installation quick and easy but also allowing future alterations or, in the event of a sheet being damaged, enabling replacement pieces to be incorporated if necessary.

Of modular build, the system allows houses to be extended as needs grow and the greenhouse is designed so that the roof can be clad with Keder material in the future should the nursery wish to do so.

Keder cladding is designed to be versatile and strong, enabling it to withstand high winds and heavy snow. The insulating properties of the cladding mean that in summer it helps reduce daytime temperatures while at night heat is retained. Indeed, trials have shown that Keder cladding gives up to 50 per cent reduction in heating costs compared with traditional glasshouses. Just like double glazing, the cladding also helps to reduce condensation.
According to Keder, the bubble design causes a considerable scattering of light — up to 83 per cent, of which 30 per cent is healthy infrared light diffused through the air bubbles. The diffused light scatters evenly to avoid problems of shade and burning within the greenhouse.

Design, construction, installation and project management were handled by Keder Greenhouse owner and managing director Colin Moore. Based in Worcestershire, this manufacturer has been building high-spec commercial houses for more than 20 years and Moore, himself a grower, understands the need to nurture and protect crops from the elements while also extending the growing season.

At Boningale, a team of six men took 12 days to complete the project. The only issues affecting construction were soil conditions and the weather. When preparing the foundations, the digging equipment hit sandstone and diamond-tipped drilling equipment was required. Later, a day-long storm filled the gutters with hailstones. "The build had to be delayed while the storm persisted," Moore recalls. "In 23 years of building Keder greenhouses, the team has never before, nor since, had to leave site due to weather — and we build in the Outer Hebrides and the highlands of Scotland."

Impressive concept

But what does the construction mean for Boningale? The nursery’s production director Penny Fryer first saw a Keder Greenhouse structure at Baginton Nurseries near Coventry and was impressed with the concept.

"We needed more space to accommodate a growing volume of production and the purpose of the house is to assist in the growing of quality plants," Fryer explains. "We went for this design so we can improve air movement."

She sums up: "The Keder provides us with an excellent growing environment for the crops. It is a robust structure with good ventilation and can be adapted to suit our growing needs and the weather."

Elsewhere on the nursery a Polybuild tunnel has recently been constructed. Measuring 4m to the eaves to enable easy access for transport purposes, and vented on one side only, the single-span tunnel holds a variety of traded stock and is another facility that helps Boningale to maintain its reputation in the provision of quality stock.

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