Should it be glass or plastic?


Hort conference Down Under provides a forum for differing views on greenhouse construction.


By Grant Ullyot T


om Baumann and two University of the Fraser Valley agricultural students recently travelled to Brisbane, Australia, for a major horticultural conference. It focused mainly on hydroponics, although many of the presentations concerned themselves with field-grown food under the cover of protective structures. Baumann says the conference concerned itself with modern covering materials, focusing heavily on glass construction, but his main interest was to compare notes, and he emphasized that plastic covered facilities, such as the new greenhouse at UFV, have some advantages over glass-enclosed structures.


His talk was well received and many questions were asked about insulation factors, light diffusion/haze factor and the longevity of the materials used. Representatives from the Wageningen Research University in Holland were on hand in support of glass enclosed facilities.


During the two days of discussions on glass versus plastics, Baumann defended plastic coverings, mentioning the potential success of the Biodome project in B.C.


Developed by Surrey resident Tom Coclough and Eco Energy Asia, it is a closed, contained and controlled environment for year-round use in any climate. Its panels are created using a special plastic film called ethylene tetrafluoroethylene to ensure light is equally spread through the structure. Because the panels are clear, they can use the sun as a natural heating source. Baumann said that even with very little comparative research available, especially when it comes to multi-layer


Tom Baumann


materials, the conference participants were keenly interested in trying the materials and there is now a trial on- going in Cairns, Australia. According to Baumann, light transmission is highest with glass and lower with plastics at this time. “Our colleagues agreed with us that production can be improved by as much as 30 per cent with light diffusion, however, why and how is not yet completely clear. But we do know that for every one per cent loss of light we lose one per cent of yield, so it matters most what light the plants can capture on their leaves.” The cost for plastics is


higher compared to regular glass and lower when considering tempered glass, which is mainly used on roofs. Double-layer plastic has the advantage over glass as there is dead airspace between layers and none in glass. Plastics also allow for better humidity and heat control. However, plastics need to be replaced after 15 years or so, depending on materials, while glass can last 50 years. “With air tightness in a greenhouse,” says Bauman, “we can potentially recapture all water (except that being sold with the fruit), making this a hit in countries with water shortage. This means all water losses form evaporation in the greenhouse and of course transpiration by the plants may be captured and re-irrigated to the


12 British Columbia Berry Grower • Spring 2016


plants. Imagine that in a desert climate. “The air tightness also allows for CO2 control at its finest. The CO2 drawn from the boiler stack injected into the greenhouse actually makes for increased production.”


Baumann further explained that with a double-layer insulation and proper attachment to the superstructure, it is possible to break all contact with the cold outside in winter or the hot outside during summer, and save lots of energy for the operation.


During a field tour, Baumann said, he was not impressed with tour participants walking between rows and touching plants and fruit.


“Food safety is so important these days and participants should know better. However, this being an international conference there were folks from countries that do not have the stringent rules that we have in Canada when it comes to food safety.” An area the group visited had a destination farm with lunch facilities, gift shops, grocery shopping and the like. Customers could tour the greenhouse, but only with a guide. Baumann said the food was superb and the place hires predominantly those with various levels of disabilities. “Growing the future of food globally, water recapturing, soft pest and disease control, great food safety and growers proud of what they are doing and proud to show it off to an international audience made for a most memorable experience. We have been invited back for 2017 and I am going to make every effort to go.”


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