What did the Romans ever do for us!
Not far from where I live in northern Scotland, Victorian gardeners used to grow pineapples and other exotic fruit! To do this required creating the right micro-climate and this was made possible by designing buildings constructed mainly using glass. Long before modern float glass technology was developed, plate or sheet glass was used, but this was very expensive and the preserve of the rich landed-gentry. However, improved plate glass production techniques changed this and greenhouses soon become features of many walled gardens up and down the land – a sort-of status symbol indicating both wealth and education. By the 1840s, they had evolved to become a new building type, which combined improved glass manufacturing technology with increasingly sophisticated cast-iron prefabricated construction. Ever-larger botanical buildings were designed, including exotic ‘palm houses’, almost alien in their architectural form, providing homes for exotic almost alien-looking plants brought back to the UK from far-flung places around the planet by dedicated ‘plant hunters’. The public loved them.
Kew Palm House, Kew Gardens, West London @kewgardens
The wonderful thing about palm houses and simple greenhouses too, is that they work passively – ie naturally – separating the internal environment from the outside by an almost invisible glass skin. No additional human intervention is required to let in sunlight while keeping out the weather. If built correctly and properly maintained, they can last for centuries (Kew Palm House and Lednice Palm House in the Czech Republic were both built in the mid nineteenth century).
Lednice Palm House, Czech Republic, part of a UNESCO World Heritage Site
The reason why glass structures work, is down to the unique properties of glass. Glass lets shortwave radiation pass through ie sunlight, which is essential to plant life, but reflects the longwave radiation (heat) given off by things that have been warmed by the sun inside the greenhouse ie walls, floors, soil, furniture, people, plants etc. Architects use this process in passive-house design, often incorporating large south-facing windows or installing conservatories to maximise internal sunshine into whole rooms, to warm masonry floors and walls and create cosy places to enjoy even during winter, without burning additional fossil fuels. Placing lean-to greenhouses against the high masonry walls of walled gardens, works the same way. The walls have good thermal capacity, absorbing the sun’s rays – ‘passively warming’. They initially store the heat then re-radiate it, as the outside air temperature drops, keeping the internal environment of the greenhouse at a higher temperature throughout the day and for longer into the night. In addition, the glass walls keep out cold winds, which can quickly strip away any heat and they allow humidity control too.
Espalier apricots on the south-facing wall of a walled garden in north Aberdeenshire. The plants are now over 100 years old.
The walled gardens of yesteryear were created primarily to optimise general food production. Exotic fruit like pineapples were an exception. Many walled gardens still function today, working passively, just as they did 100 years ago when first built.
In the above photo of a restored Victorian lean-to greenhouse in England, the vines are planted outside, so are watered naturally by the rain (both directly and by rainwater catchment – passive systems). The vines are trained through openings low down in the greenhouse masonry wall and grow within the greenhouse itself. If necessary, the short length of stem exposed to the fresh air can easily be protected by horticultural fleece. These vines benefit from the naturally increased warmth within the greenhouse, passively increasing the sugar content of the fruit.
One of many humidity-controlled glass-houses at Kew Gardens, West London @kewgardens
Humidity control is required to grow exotic plants and trees from other regions where the climate is much warmer, much wetter or much drier. With regard to growing pineapples in Scotland, the passively heated greenhouses of the time were adapted as they required additional heating / energy input. In Victorian times this meant a coal or wood-fired furnace near-by, delivering hot air or hot water to the greenhouse to create consistently warmer conditions. Although there are ways to passively heat greenhouses to higher temperatures without burning fossil fuels, such systems are more expensive to build and operate. Perhaps we should simply eat seasonally and locally! Pineapples can be reserved as a holiday treat! This still leaves plenty of choice throughout the year here in the UK from plants and veg that can be grown passively, especially if we store and preserve our produce. This is still what happens in many European countries.
Kew Gardens in West London now has a wide range of glass-skinned buildings, from the original Palm house opened in 1840, to a range of modern glass and steel structures built during the last 50 years following the advent of float glass technology. These buildings generally contain plants requiring a variety of modified environments such as consistently warmer temperatures and a variety of humidities. The ideas behind passive design have become necessarily watered down. All-glass structures can frequently overheat leading to the need for controllable blinds or whitewash solutions being applied to the glass internally – both solutions due to too much glass! But these buildings are there to exhibit a wide range of plants for the public to see and enjoy and for educational purposes, so compromises are necessary.
Eden Project Biomes @edenprojectcornwall
Perhaps the ultimate structures for growing and seeing plants are the biomes of the Eden Project in Cornwall. They are an astonishing achievement, of breathtaking scale. This is something that can only be appreciated by visiting. Set in a relandscaped quarry, they are truly ‘otherworldly’. Their design uses a translucent skin and is a reminder that modifying the environment in this way, using translucent materials to improve growing conditions, apparently dates back to Roman times. As once said in a Monty Python sketch, ‘What did the Romans ever do for us’!
The above Text and all Photographs are copyright of Wincenty (Wicek) Sosna. Please contact SeeHow for permission to reproduce in any way, in part or as the complete text.