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Opinion is divided as to who built the first glasshouse, and whether it was the invention of putty or the introduction of factory-produced glass that enabled greenhouse design to advance so quickly during the 18th and 19th centuries. Few would deny, however, that a greenhouse can be found at the heart of almost every serious garden, whether it’s an ornamental place for growing pot plants, orchids or alpines;a structure for the production of culinary delights such as peaches, grapes, cucumbers and pine-apples; or as a powerhouse for plant propagation, filled with seedlings and rooting cuttings.
Traditionally, wooden houses have been preferred for aesthetic reasons and for growing specialist plants such as alpines and orchids, on account of their buoyant atmospheres and flexi-bility of size and shape, but earlier models needed almost constant repair and treatment of the wood. Metal houses, on the other hand, were for more serious growers in production horticulture, but they heated up and cooled down so quickly that many less forgiving plants simply refused to grow in them.
Nowadays, both wooden and metal houses have been improved beyond all recognition, so that the choice of one or the other has ceased to involve anything other than personal preference. The latest powder-coated aluminium glasshouses, modelled on traditional styles with elegant mouldings, even give you the look of a painted Victorian greenhouse without the associated maintenance programme required for wood. So what should you look for when choosing a new greenhouse?
Site and size
Begin by choosing a site. It should be firm and level, unobstructed by overhanging trees and convenient for installing services such as water and electricity. Orientation is not critical. Decide on the size of glass-house that you need and then double it-plants will expand to fill the space available.
To grow groups of plants that require significantly different conditions from each other under the same roof, install partitions with appropriate heating regimes within each one. A large greenhouse will need adequate concrete or brick foundations; the atmosphere within the house will be significantly improved if it has a base wall of brick or stone. The finished floor should be easy to sweep or rake free of fallen leaves, spilt compost and so on-tiles, stone slabs or gravel, for example.
Consider climate zones
The type of plants you want to grow will dictate the amount of heating required. Alpines and summer crops such as tomatoes don’t need additional heat, but ‘hothouse’ plants such as orchids, palms and peaches will need more warmth than the British climate can provide. Conven-tional hot-water pipes heat up and cool down slowly, maintaining a more balanced environment; electric heating is quick to respond, but tends to create a drier atmosphere. Keep fuel consumption under control by using supplementary insulation, reducing draughts and adding frames within the main house to create microclimates where required.
Ventilation and shade
Ventilation and air flow are crucial install vents not just in the roof, but also in the side walls of the greenhouse, so that fresh air can enter as hot air escapes. If the greenhouse is to be left to its own devices during the day, automatic ventilation should be a priority. Fans may be used to improve air circulation, distributing heat evenly throughout the house, preventing the build-up of condensation and helping with the control of fungal diseases. Shading is often overlooked, but it can make a huge difference, pre-venting overheating by day but providing extra overnight insulation if necessary. Shading works most effectively when fixed to the outside of the greenhouse.
Remember the services
There must, of course, be water on site; this could be mains tapwater or rainwater collected from the roof and stored in tanks within or beneath the house. Most plants prefer rainwater, especially in areas where tapwater has a heavy lime content. Com-puter technology can be used to control almost every aspect of a greenhouse atmosphere, from carbon-dioxide content to humidity, with adjustments to regulate temperature, ventilation, shading and watering. Finally, don’t forget to invest in good-quality staging benches: the most comfortable are handmade to suit the height of the user. Rolling benches are a good solution if space is at a premium.
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