A zoo may sound like the last place you would expect to find cutting-edge horticulture. But Paignton Zoo Environmental Park in Devon is pioneering what it describes as a "revolutionary" system to maximise crop yields in a tight space, which could open the door to large-scale "high-rise" growing worldwide.
"We have the first commercially viable vertical growing facility," says Tom Bentley, business development manager at Valcent, developer of the VertiCrop system.
The zoo's curator Kevin Frediani, who has also managed collections at Cambridge University Botanic Garden and Amsterdam Zoo, describes the partnership with the growing technology company as "a happy accident" thanks to a chance meeting at an event where Valcent was exhibiting a model of a vertical hydroponic system, which was then still at an experimental stage.
"We hadn't even thought about zoos as a market for this," says Bentley. "This is a pilot as well as a commercial operation; it lets us calculate the cost per square metre."
Valcent is headquartered in Vancouver, Canada, with a UK base in Cornwall set up to access markets in Europe, North Africa and the Middle East.
A Valcent office in Texas is "in mothballs", Bentley adds. "They did a lot of research to establish the viability of VertiCrop but didn't make it marketable."
Already the company has demonstrated the VertiCrop system at the IPM Dubai trade show, where it generated "a huge amount of interest", says Bentley.
Frediani explains the zoo's particular growing requirements: "Space is at a premium here and food is one of our biggest costs. We wanted a sustainable system, which meant low-input, high-output growing. Production also had to be flexible, with minimal wastage. And it must pay its way by replacing bought-in food, which costs us over £200,000 a year."
The 3m-high glasshouse is on the site of a former goat paddock in the middle of the zoo — and it certainly has a small footprint, at just 120sq m. Inside, the most striking feature is that it the crops are in constant motion, on a single rail looping around the whole greenhouse area, taking 40 minutes to complete a circuit.
Valcent's horticultural manager Grahame Dunling explains: "The plants benefit from different areas of sun and shade and the movement also reduces mildew and other diseases."
Each of the 70 rigs consists of eight levels, each with two different-sized trays. The purpose-built trays are adaptable to different crops and include funnels though which water and nutrients are dispensed from nozzles attached to a dosing unit.
Frediani describes the system as "a cross between ebb-and-flow hydroponics and aeroponics" as the roots are not constantly immersed in water. Growing in trays "maximises the water and nutrient availability, while minimising chemical use and wastage", Bentley adds.
Run-off is collected in a central floor drain, filtered through UV light before being recycled into the system. Soluble feed mix is added at a rate of 5kg per 80 litres.
Rather than Rockwool, the system uses US-manufactured Sure To Grow hydroponic media made from lyocell, a cellulose fibre derived from wood that, once used, can be fed to the animals.
The format also allows smaller crops such as culinary herbs to be grown directly onto InseroMat capillary matting from Kent-based InseroTech. The crop is irrigated from the reservoir in the tray by a wick and can also be used afterwards as a feedstuff.
A single touch-screen monitor linked to a Priva computer provides control over irrigation, ventilation and conveying. According to Cambridge Glasshouse Company technical services manager Ian Angus: "You can select which group of five rigs you want to water and for how long."
The screen controls the gas-powered underfloor heating; a double-skinned roof ensures that energy consumption is similar to a conventional glasshouse, Angus adds. "As crops are more intensively grown, the cost per unit of output is significantly less."
The system is also compatible with integrated pest management (IPM). According to Frediani: "We're implementing IPM throughout the zoo, and the glasshouse will be a clean-room environment."
Crops are harvested from rigs with a purpose-built handler that allows trays to be loaded and unloaded four-at-a-time at the operator's waist level. Dunling says: "We are working with Visser to develop a fully automated version for the commercial grower."
So far, the zoo has concentrated on growing lettuce — specifically the varieties Roxy, Kuala, Charita and Estelle. "Two grew well, while two got too leggy but are fibrous and tough," says Frediani. "What suits the human eye is different from what suits the animal's belly. And as the zoo gets through around 800 lettuces per week, costing £9,000 a year, we are already eating into our costs."
The system can potentially grow 11,200 lettuce plants at once, compared with 4,332 in conventional "2-D" cropping, says Dunling. The plants are ready for harvesting in five weeks. "It means you need to think five to 10 weeks ahead," says Frediani.
Other potential crops range from strawberries, rocket and watercress to plants entirely new to hydroponic cultivation such as Montia perfoliata (miner's lettuce), Asarum canadense (Canadian wild ginger or snakeroot) and Houttuynia cordata (lizard tail), which Frediani describes as "high in vitamin C and an alternative to cabbage".
The team has experimented with ornamental crops too, though Frediani points out that plants such as pansies and nasturtiums also have a role in providing "enrichment" of animals' diets.
A webcam on the glasshouse ceiling will provide a live feed on the zoo's website. "It's good for operators too as it lets them see what's happening on top," Dunling adds.
Visitors will also get a glimpse of goings-on inside the glasshouse. "It's all on show," says Frediani. "We want to educate visitors about the issues around food and growing."
Looking to the future
As yet, the glasshouse has no supplemental lighting, but the possibility of incorporating LEDs is being explored with manufacturer Philips. "The cropping density makes technologies such as supplemental lighting more affordable, as you need fewer per square metre," says Bentley.
"Our whole focus is on cost per cubic metre of growing area. Growers won't use the system if they have a lot of space to grow in. But for those who can't expand horizontally, it will allow them to expand vertically."
Frediani adds that demand for high-density growing systems can only increase. "There will be another two billion people on the planet by 2050 and we will require an area the size of Brazil to feed them."
Bentley agrees: "Everyone is realising we need new forms of agriculture. Obvious applications include deserts and other non-arable land — including cities."
Furthermore, the cost-effective artificial lighting would allow for closed-box production in warehouses, he adds. "You could take it anywhere in the world and grow crops all year round."
He acknowledges that commercial growers are concerned about the cost of the system. "But there are niche markets here in Britain. And supermarkets increasingly want produce from close to home — 12 months of the year.
"All kinds of people have come to us that we wouldn't have thought of. Governments are looking to solve issues of food security. We are talking to sheikhs in the Middle East — and their response to this tells us we are on the right track."
Having control of its own food supply means that Paignton Zoo Environmental Park will be able to improve its animals' diet with plants that are not otherwise available to the zoo, which may be higher in fibre of nutritional value to them.
Curator Kevin Frediani explains: "The challenge is to stimulate natural behaviour in a captive environment and part of that is their interaction with plants."