Largest greenhouse complex (botanic garden)

Opened in March 2001, the largest greenhouse complex at a botanic garden is the series of eight interlinked geodesic domes covering a total of 2.25 ha (5.6 acres) at the Eden Project near St Austell in Cornwall, UK. The largest of these – the tropical Rainforest Biome – stands 55 m (180 ft) tall at its apex, 110 m (361 ft) in diameter and has a footprint of 1.6 ha (4 acres). The connected more temperate Mediterranean Biome is 35 m (115 ft) tall, 65 m (213 ft) across and covers an area of 0.65 ha (1.6 acres).

Designed by British architect Nicholas Grimshaw and engineers of Anthony Hunt Associates, the biomes are constructed of geodesic steel frames carrying geometric panels of insulative ETFE (ethylene tetrafluoroethylene) thermoplastic: 625 hexagons, 16 pentagons and 190 triangles. The two biomes are joined via the grass-covered “Link” building.

The Eden Project is home to approximately 2 million plants from across more than 5,000 species – much of that diversity is afforded by the range of ecosystems provided by the climate-controlled greenhouses. The Rainforest Biome is maintained at a temperature of 18–35°C (64–95°F) year round and hosts everything from vines and bananas to coffee and pitcher plants, while the Mediterranean Biome is kept at 9–25°C (48–77°F) and houses, among other things, grape vines, cacti and citrus trees.

In 2023, the Eden Project’s greenhouses (as well as other facilities) began to be heated by geothermal energy collected using a 25-cm-wide (10-in) pipe that stretches 4.87 km (3 mi) underground. It's believed this will enable the site to stop using almost all gas and will save approximately 500 tonnes of carbon dioxide per year.