Being a typical adult male, I spend my life watching my weight, hoping that the scales don’t say ouch. Salads are a way of life whilst calorie counting. Part of the salad is of course, a red tomato. The significance of the one I was eating was that it was actually produced here in the Vale of Evesham. Bearing in mind that we are in early April, the fact that we are producing tomatoes in the Vale of Evesham is quite a feat, worthy of some further investigation.
There are a few specialist growers in the Vale who produce long season tomatoes using Hydroponics, sometimes called Nutrient Film Technique. Briefly to explain how the system works, there are long channels in a greenhouse which have water continually pumped into them. The channels are sloped gently so that the water flows down, from where it drains back into an underground tank. Tomato plants grow in rock wool blocks, which sit in this channel of water so that they can take up both water and nutrients as required, creating an almost perfect environment for the roots to grow in. Surplus water is then passed back into the underground tank, where it is boosted with more fertiliser and acid so that its Ph is maintained at a level of approximately 6.7, to allow trace elements to be made available for uptake from solution by the plant.
Modern greenhouses tend to be very large, the latest ones have a height of approximately seven metres. The newest one in the Vale of Evesham is located at Offenham, and others are planned for the Vale. This nursery extends to an area of approximately 4 acres, of which 2 acres is new. The greenhouse height is needed to allow the crop to grow in an environment which has enough air movement around the crop to keep it healthy. The nutrient channels are suspended from the greenhouse structure in metal channels, some three to four feet above the ground. This creates a more pleasant working environment for the crop workers, as they are picking fruit at waist height, rather than from the ground level, which can be back breaking.
The crop then grows to a height of approximately three metres, supported by string, wound onto a wire bobbin. As the plant grows up, the string is wound off the bobbin, twisted around the plant’s stem, while the side shoots are taken out, leaving just the main stem to create the plant. This process happens every week, allowing each tomato plant to grow to a length of approximately 25 metres over the season. As the stems become longer, they are supported by brackets which prevent them from being damaged by passing trollies. Plant health is also maintained by having plenty of air circulating around the bundle of stems, using large circulating fans with ducts so that all parts of the greenhouse are of a uniform temperature.
Growing operations carry on year round. Lighting is provided by LED lighting within the crop canopy, and high pressure sodium bulbs at high level, to provide enough light to maintain active growth all year round. The LED’s are specifically designed to maximise light absorption in the photosynthetically active region of the light spectrum.
Pollination is undertaken by bumble bees, and insect control is by a range of biological predators such as Encarsia Formosa, Phytoselius Persimilis and Macrolophus. It has reached the point where virtually no insecticides are used in the growing area.
Product handling within the greenhouse is also well thought out. Crop workers use hydraulically operated working platforms to reach the top of the plants. Picking trollies are used to remove fruit from the rows, all are supported on the heating pipes, which also serves to form a railway down each row. All feed back onto a central concrete path, allowing efficient removal of fruit from the greenhouse, using pallets and the ever efficient fork lift.
I am sure you can imagine, to support a glasshouse of this size, you need a significantly large plant room to house all the equipment needed, and it is here where the green part of the production really takes place. There are two sources of heat. One is a combined heat and power plant, where electricity is generated using a large gas powered engine to run a generator. Electricity is then used to run the supplementary lights. The other back up heat source is an extremely large gas operated boiler, with flue gas condenser mounted on the chimney. This is also capable of generating copious amounts of hot water. The flue gas condenser captures as much heat as possible from the flue gases, to ensure maximum operating efficiency.
Either the generator or the boiler is run during the day, so that the greenhouse can utilise the flue and exhaust gases as a fertiliser. Once scrubbed in a urea formaldehyde solution, a mixture of almost neat carbon dioxide and air is then pumped into the greenhouse, where it is absorbed by the plants to create tomatoes. Surplus heat generated during the day is stored in vast hot water cylinders, affectionately known as dump tanks. When the environmental computer calls for heat during the night, to keep the growing areas up to temperature, hot water is pumped from the dump tanks, rather than run the boiler again. By using the exhaust fumes from the generator and the flue gas condenser on the boiler, dump tanks, and Carbon Dioxide, very high energy efficiencies are achieved, running into 90% efficiency.
The drive for greater economies on these glass house nurseries is relentless. At the moment, one owner of a local nursery, has constructed a series of anaerobic digesters, so that all the green waste can be converted into methane. Enormous fermenting tanks have been constructed to house the green waste. Ideal conditions are created to allow bacteria to break the organic matter down. The gas given off is collected, cleaned, and then used to run a boiler or generator, thus completing the cycle.
It is quite foreseeable that these horticultural nurseries will be carbon neutral once they have a digester operating next to a modern glasshouse complex. Not only that, but if they are located close to a household refuse site, there is no reason why further green waste from households could not also be treated in the same way, so that maximum gas is produced, perhaps even surplus to the site’s needs. When this happens, then gas is actually exported into the local grid, thereby helping other energy users in the immediate vicinity.
These horticultural nurseries are amazing facilities to look at and local growers occasionally open their nurseries at various times to show people what they do. If ever you get a chance to take a look, it is very much a worthwhile visit, particularly to see how modern horticulture can operate in harmony with their environment, whilst still producing large quantities of fruit which feed us. Surely this must be a win win position for us as a country, both in the short term and the long term.
Tony Rowland BSc(Hons) MSc MRICS