Restoration at Kew Gardens: the temperate house

Kew Gardens was the horticultural pride of nineteenth century England, and indeed still is England's gardening pride now.  Beginning in the eighteenth century on land donated by King George the Third,a king with a keen interest in horticulture, this arboretum, a garden devoted to trees, flourished through a combination of royal patronage, scientific commitment and devotion from the British public, ever keen on beautiful gardens. It is, as far as I know, the only botanical garden with its own police force, constables who deal with minor infringements and who perform a patrol and ranger service, but who are rarely called to use their powers. 

Sister to the smaller Palm House, the Temperate House, which is the largest Victorian glasshouse in the world,  was constructed on a mound 1.8 metres high composed of gravel and sand spare after Kew's lake was excavated. The Thames Valley has extensive gravel and sand deposits. Work on the Temperate House began in 1860 and it was opened to the public in 1863, but completion took another forty years. The construction took 4880 metres of steel, and well over an acre of glass. Like all Victorian glasshouse structures the windows are relatively narrow compared with modern structures, reflecting the less developed technology of that age compared to now.In some ways the narrow windows in the roof reflect the design of the original Paxton house, the first greenhouse design, and the design is the high point of Victorian glasshouse technology

Decimus Burton, the architect who constructed it, made a serious botanical error in its design, for he installed windows of tinted green glass, thinking that green light  was good for plants, whereas it is not, for plants cannot use it for  photosynthesis, which is why they reflect it and are green. The original glass had to be replaced and plants afterwards thrived.But Burton installed the state of the art heating system of his age, a massive coal powered system, whose chimneys were hidden by the large, supposedly ornamental urns that adorned the edge of the roof. Moreover, the ventilation was by a manual pulley system still found in older glasshouses. 

The Victorian Age was a time when plants were brought to Britain from across the empire, and the ever intellectually curious Victorians committed to scientific endeavour. Thus the Temperate House thrived  and was a major attraction for the culturally hungry British public. Even a few bombs dropped in World War Two did not do much damage, because they were not direct hits, but it was time that worked even stronger ravages and by the start of this  millenium refurbishment was needed. 

Planning the refurbishment took many years, and a well-known firm of conservation architects were employed to design the process. Critical to the project was protecting the plants, some of which are rare specimens being preserved at Kew. Let's take the example of Encepahallartes woodsii. This cycad, a member of a  relict order of trees superficially similar to palms, that  thrived in the Jurassic period, but no part of which is edible [ Cycadales are poisonous in fact] is very rare in the wild and only males are known to exist now. So botanists are searching for a female, unsuccessfully yet, so it is necessary to preserve the surviving male specimens, while the search continues, else a species will be lost. Some plants were cocooned in protective fabric when necessary, others taken to specially constructed nurseries, but the whole structure was encased in a massive tent one hundred and ninety metres long, the length of the Boeing 747s.  Constructed on a scaffolding frame, it used polythene protective covers. Obviously the tent had to be taller than the glasshouse, so it was an exercise in massive construction. 

The figures are impressive. The programme took five years from commencement of work, beginning in 2013 to its completion in 2018. As the structure was large the total length of the scaffolding required for the tent and other purposes was one hundred and eighty kilometres.   Six thousand one hundred and ninety one panes of glass were replaced. Fourteen thousand square metres of metalwork were painted, using five hundred and eighty litres of paint. The great steel nuts and bolts were taken out and where possible cleaned of rust, and where not, replaced. 

Cranes were needed to take down the large urns and statuary and install new ventilation pipes in the roof. A modern heating system was installed and along with a new ventilation system it was computer controlled. While the  thousand plus panes of glass were being replaced the ironwork restored to its former glory. 

The architects then faced a tricky problem. After completion they tested the building with an artificial rain storm, only to find that it was leaking in many places. This led them to realize that they had assumed that the structure was built true, but like many older buildings it was not. This showed that the Victorian glaziers had exercised considerable skill in fitting the glass to the frame. The problem was resolved by careful application of leak prevention strategies, which  involved fitting pieces of glss into the holes, many of which were tiny. 

Inside the Temperate House paths were renewed and the central area redesigned to make it easier for the general public to move around.  

There are about ten thousand plants in the glasshouse, so I can only mention but a few. 

Musella lasiocarpa, the lotus flowered banana, so named because its flower resemble a lotus flower, is an Asian plant which is used as a source of healing herbs and its leaves are used for weaving fabrics. In an age when manmade fibres are becoming less viable, as they are oil-based, we will need natural alternatives. The plant is good for erosion control on steep hillsides, as it has strong and widespread roots. 

Another plant with medicinal use is Dioscorea deltoidea, the Nepal yam. This is an indeible yam,but its roots, vigorous rhizomes, are a source of steroids with medicinal uses, some of which are anti-inflammatories.  Kew is preserving this plant so that its seeds can be collected and used in medicinal research. 

Some are extinct in the wild. Take the case of Abutila pitcairnense, the yellow fatu. Native to Pitcairn Island in the Pacific, the refuge of the Bounty Mutineers, it is extinct in its native home due to predation by goats and rats, and its only home is now Kew. Another endangered one is Banksia brownii, which is an Australian plant with reddish brown flowers  whose seeds break their dormancy in bushfires, which serve to spread them. In its native land it is endangered by development, so its being protected at Kew.   

Or let's turn to the tree on whose leaves  Robinson Crusoe might have looked. Alexander Selkirk, a privateer [legal pirate permitted to raid the king's enemies] had no confidence in his equally villainous, but incompetent  captain and so asked to be marooned on Juan Fernandez Island off South America, where he remained three and a half years. He was wise, for the ship sank and the crew were captured by the Spanish, who were not pleased with English pirates..There Selkirk, one of the men on whom Defoe based his tale of Robinson Crusoe, fed on goats introduced to the island as food supplies by British privateers and whatever else he could eat. The cabbage tree, Dendroseris lioralis, has large cabbage shaped leaves which are excellent goat food, though they are too rubbery for humans to digest. Found only on Juan Fernandez this small, easily cultivatable  tree is easily stripped of its leaves by goats, so it is being propagated at Kew. By the way, the name cabbage tree is a popular colloquial, non-scientific name applied to a few different species of tree.

Ten thousand species is  more than I can detail here, but I hope that you can get a taste of the Temperate House, a sip from the wine cellar of horticultural glory.It opens tomorrow, fifth of May 2018, in time for the Spring bank holiday weekend. Expect it to be busy!