Temperate House, Royal Botanic Gardens, Kew

20180503_112916When Decimus Burton’s extraordinary Palm House opened at Kew in 1844, the world gasped. Burton’s star, already in the ascendant, had reached dizzying heights.

Glory was all very nice, but now he faced a challenge. How on earth could he top innovation on that scale? Kew’s magnificent Temperate House, twice the size of the Palm House and still the world’s largest surviving Victorian glasshouse, saw Burton outshine even himself. The first, central block was opened in 1863, filled with the results of Kew’s active plant-collecting programme – and a few surprises of its own. Underfloor heating, drainpipes concealed in the building’s very pillars and a boiler with chimneys cunningly hidden inside ornamental urns on the roof were just some of Burton’s mon-cons. The north and south extensions arrived in 1888/9 adding more glass, more ideas and more plants.


(c) Royal Botanic Gardens, Kew

By the early 21st Century, however, the Temperate House was showing its age. Any 150 year-old glasshouse would need work, but this one was also a victim of its own cutting-edge technology. Water had seeped through Burton’s concealed metal drainpipes, accelerating rust, and areas were becoming unsafe. “The balcony had to be closed,” says Georgie Darroch, the project’s coordinator. “The north octagon’s wooden beams had scaffolding holding them up.” A well-meaning 1970s restoration had compounded some problems and created a few new ones.  “They changed the heating pipes and only had perimeter radiators,” says Darroch. The original path layout was also changed, making the route narrower and more winding. Romantic, perhaps, but an accessibility nightmare.

TEMPERATE HOUSE restoration_003
(c) Royal Botanic Gardens, Kew

In 2013 the entire building was closed for full restoration.  Over £15m, much from the Heritage Lottery Fund, was set aside and heritage architects Donald Insall Associates charged with bringing the Temperate House back to Victorian splendour.

“It’s a Grade 1 listed building,” says Georgie Darroch, “so the fabric of the building had to be restored in the most sensitive manner possible. It had been built on a pedestal of detritus from Kew Lake. Old pipes, bits of glass clinker – we even found some original shards of glass. They thought green-tinted glass would be better for the light. It didn’t last long.” Archaeologists found 19th century bed-walls, along with Decimus Burton’s famous heating pipes.  “They’re enormous,” says Darroch. “They look like they were used yesterday.”


(c) Royal Botanic Gardens, Kew

However fresh-looking, Burton’s pipes are not suitable today. They have been conserved and re-covered and a new biomass heating system installed under the original gratings. Sterile wood pellets are used; “we don’t want to bring in anything with pathogens.” A building management system automatically opens and closes the windows according to temperature, avoiding overheating and condensation. Damage inside the pillars is controlled with a cathodic protection system.

(c) Royal Botanic Gardens, Kew

Burton’s original glazing had wooden bars but constant shrinkage and expansion from water and heat saw them replaced with aluminium. Conservators have stripped the paint back to metal, sealed it and added anticorrosion treatment and primer before applying the final coat. Paint analysis shows thirteen different layers, including peppermint, ‘municipal’ green, and a pale ‘St Pancras Station’ blue but because the building was built in stages, the centre had already seen colour changes before the other blocks were built, so there isn’t a single ‘original colour’. A classic heritage cream has been chosen for this incarnation.

20180503_113253The west face of the building is very ornate, with ornamental friezes and two important statues, Flora and Sylvanus. Both were in poor condition – “Flora had lost her toes,” admits Darroch. Just four of the 116 urns – the corner chimneys – are original. The others are now lost, replaced by 1970s castings in reconstituted stone, also restored.20180503_120526

Fifteen thousand panes of glass have been replaced. Each will continue to be cleaned by hand, though built-in hooks are no longer health and safety compliant; a mobile elevated platform will be used instead.

20180503_113020Inside, the paths have been widened and straightened to look more like the original promenade-style layout and for ease of access. The 1970s redesign included pools; this one sees entirely new water features.

20180503_113113In all, 69,000 individual elements were removed and cleaned, repaired or replaced inside the temporary tent-like covering regular visitors have got used to seeing the outside of, so work could continue in all weather. “We were running out of time,” admits Georgie Dunnoch. “We didn’t know the full extent of the damage until it had been stripped back. The seventies restoration used a lot of filler. It looked ok from the outside but hadn’t lasted. There was more work more than anticipated and we had different teams working in the same place at the same time.”

20180503_113253The different teams had very different needs. Scott Taylor, lead horticulturalist, was in charge of the plants that are the Temperate House’s raison d’être. Most had to be moved, a delicate job when dealing with specimens as old as the building itself. “We have a Ceratozamia Mexicana from 1880 and a Chamaedorea pochutlensis from 1889,” says Scott Taylor. “Neither are particularly large so we lifted them prior to works commencing and transferred them into our nurseries. A large Dioon meijiae and Cycas revolute may both be around 150 years old but a number of records were lost many years ago so we can’t be sure. We also have plants propagated from original stock and regrown as cuttings, seedlings etc. These include Acacias, Luculia and Rhododendrons.

E. woodii 1
(c) Royal Botanic Gardens, Kew

The largest specimens were root-pruned as early as possible, preferably at least a year before lifting. We start by cutting one side of the desired rootball size, let the plant heal for up to 3 month then cut another side and so on until the whole rootball has been pruned. The time delay between each side allows fine roots to form and lessens the stress on the plant. Once the rootball is prepared we undercut as far as possible and then lift with a telehandler (a kind of fork-lift truck) into a pot.

“We had the use of several nurseries. The largest plants (tree ferns, palms, cycads, camellias, rhododendrons, bamboos and others) were placed in our tallest space which had all the fittings (heat, shading, venting, water etc.) needed to care for plants.

Luckily we didn’t lose too much and, thanks to resources like the Millennium seedbank, we have managed to replace lost plants. This has also allowed us to review the collection and add new plants we have never grown before. As we were emptying the house and removing the canopy seedlings sprang up from the ground including Calceolarias and Rehmannias, previously shaded out by trees and shrubs.”

(c)Royal Botanic Gardens, Kew

Some specimens were just too big to shift. “We left ten plants in situ, all palms or cycads,” says Taylor. “A scaffold was built around them then wrapped in plastic with heaters and grow-lights inside. A member of staff visited them up to three times a week for watering and monitoring. Despite all this care they were still quite dusty. We hosed them down once the protection came off.”

New features include a tree fern gulley and palms, from the Phoenix roebelenii in the north end to the Chambeyronia macrocarpa, Jubaea chilensis and Butias in the centre block but, like all gardens, it is a work in progress. Younger specimens will take time to fill out, such as Brahea armata, Livistona carinensis and Rhopalostylis sapida.

Much like the Temperate House’s first, Victorian visitors, we will have to exercise patience – and visit often.






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