Beyond the border: Greenhouses

Kew Gardens, above, to the Eden Project, green-houses rule the plant world.

Tiberius had a taste for cucumbers. He craved a daily helping of the crunchy green vegetable. But even Roman emperors couldn't get them to grow out of season - until he found that planting them under sheets of a translucent mineral called mica ensured a regular crop. Thus the greenhouse effect was discovered.

Glass, the main component of greenhouses, had been produced by the Egyptians 2,500 years earlier. They made ornamental beads by smelting soda ash and coarse sand. But it took a lot longer to master the mysterious alchemy of this strange material and put it to horticultural uses. Though it appears solid, in its structure, glass most closely resembles a liquid.

As explorers and traders brought back exotic plants from abroad, the greenhouse evolved as a means of keeping them alive. Elaborate orangeries sprung up in the mid-1600s as the French refined plate glass-making. It was hugely expensive, but that didn't deter Louis XIV. The Palace at Versailles, 500ft long and 45ft high, was the grandest example of glazing yet seen.

Industrialisation enabled designers to think big. Richard Turner's Palm House at Kew Gardens, completed in 1848, had 16,000 panes of glass and 10 miles of glazing bars. The Crystal Palace, built for the Great Exhibition of 1851 in Hyde Park and moved the following year to Sydenham Hill, where it burned down in 1936, was the grandest.

Greenhouses offer a kind of supercharged gardening. Heat, light and moisture can be controlled, enabling native plants to grow out of season and tropical species to be acclimatised.

But two years ago something emerged from a disused clay pit in Cornwall to revolutionise this simple principle. The Eden Project is made of hexagonal sheets of ethylenetetraflouroethylene-copolymer (ETFE), one hundredth the weight of glass, so its construction is as light as the air inside it. Twenty two thousand square metres - all under one roof. Now that's what I call a greenhouse.

Greenhouses to visitKew Gardens palm house. Completed in 1848, completely renovated in the 1980s, it is home to a cycad sent to the gardens in 1775, which is possibly the oldest pot plant in the world.Eden Project, near St Austell, Cornwall. The biggest, most spectacular, greenhouse in the world.Birmingham Botanical Gardens, dating from 1852, with cactus house, orangery, palms and fruits.

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