New developments in greenhouses

Press, 7 April 1978, Page 9

New developments in greenhouses

A recent greenhouse field day organised by Mr Geoff Mavromatis, of the Ministry of Agriculture and Fisheries, showed some of the new developments in an already sophisticated field.

That 140 growers and other interested people were present demonstrated the tremendous interest in greenhouses and associated equipment. The use of automatic ventilation in greenhouses has been slow to catch on in Canterbury. The reasons for this are not clear. Mr Bill Brandenburg, trom the Ministry of Agriculture and Fisheries, spelled out the advantages and even when the costs were bandied around, the slow take-up of this simple, effective development is hard to understand.

Basically the system revolves around a water ram connected to a solenoid, in turn connected to a thermostat with settings enabling opening and closing in a number of stages. The total cost of the system is around $3OO and for this a much improved control of the greenhouse environment is obtained. Carbon dioxide is a naturally occurring gas vital for the growth of plants. In a greenhouse situation a new system has been developed for increasing the natural carbon dioxide

levels. This gives better growth of glasshouse crops and is particularly useful for saving precious fuel over the winter and spring months.

The way this is done in Canterbury is by burning a special type of kerosene. The gas given off is maintained in the atmosphere by keeping ventilators closed, producing an atmosphere three times richer in carbon dioxide than normal. The same situation can b- produced by releasing liquid bottled carbon dioxide direct into the glasshouse. The Fletcher greenhouse has been around for about three years and a number of these houses have been erected. There were mixed reactions to the Durolite covered structures, which now cost $41.58 per square metre (erected). Some doubts were expressed over condensation drip problems and ventilation and light transmission after a number of years, but there was no doubting the advantages of no

maintenance and improved heat retention.

The age of plastics has also seen the development of the oddly called “tunnel house.” Rather than a dark underground passage, the polythene tunnel is a light airy structure, which is simple and cheap to erect. A new development in this field has been the use of wooden laminated arches to support the polythene or E.V.A. sheeting. Light and strong, the whole structure can be erected for under $lO per square metre, so it is not surprising that a large area in England and Europe is now covered by polythene tunnels.

The conventional glasshouse still lives. Drastically changed from the old wooden structure with small panes. modern houses are tending to be metal structures and the glass panes are getting larger all the time. The field day party visited an example — where a 2000 square metre house was being erected. An aluminium and steel structure with very large panes, the price tag close to $43 per square metre did not seem to shock too many of the field day participants.

With automatic ventilation, light meters to control automatic watering, carbon dioxi e enrichment equipment, one wonders where people fit in. Certainly sophistication is the name of the game in the greenhouse industry.

The accompanying item on new developments in the greenhouse field was written by G. I. Langford, horticultural advisory officer with the Ministry o' Agriculture in Christchurch.