Mitchell Park Horticultural Conservatory (The Domes)

Mitchell Park, laid out by the landscape architect Warren Manning, a protégé of Frederick Law Olmsted, gained its first conservatory in 1898. Built under the supervision of the architect Henry C. Koch as a tribute to London's Crystal Palace, it remained in use until 1955, when it was razed to make way for a modern replacement. Its ornamental entry gates, forged by Cyril Colnik, are now displayed in the Show Dome together with bricks from the old building.

Also in 1955, a design competition drew 33 entrants and was won by Donald L. Grieb, a traditionally trained Milwaukee architect, with a scheme for three beehive-shaped domes. Construction began in 1959 and proceeded in six stages: the Floral Show Dome opened in December 1964, the Tropical Dome in February 1966 and the Desert Dome in autumn 1967. The project cost $4.5 million, and Lady Bird Johnson dedicated the domes in 1965.

In 2006 an explosion at the nearby Falk Corporation plant required extensive glass replacement, and cracked panels led to a closure of several months in 2008. On February 8, 2016, the domes closed over structural safety concerns, reopening before the end of that year. A 2019 study that raised the option of demolition was criticised by the National Trust for Historic Preservation, which had named the domes a National Treasure in 2017. In autumn 2024 the Milwaukee County Board unanimously approved the Domes Reimagined plan, whose funding was still being assembled in 2025–2026, and the domes were added to the Wisconsin State Register of Historic Places in 2026.

The three domes are conoidal rather than geodesic: their beehive profile, which the institution describes as unique in the world, rises 85 feet (about 26 m, or seven storeys) over a base 140 feet (about 43 m) across. Each provides roughly 15,000 square feet (about 1,400 m²) of growing space, one acre under glass in all.

The skin is made of some 6,000 triangular panes, 2,000 per dome, of quarter-inch wire glass that admits more than 85 per cent of daylight. They sit on a frame of aluminium tubing whose expansion and contraction with the temperature produces faint clicking sounds inside. Four one-million-BTU boilers heat the complex, and the air in each dome is exchanged in about three and a half minutes. Seven production greenhouses, six of them for growing and propagation, stand behind the domes.

The Tropical Dome holds around a thousand species: fruiting plants such as banana, papaya, ackee, guava, avocado and cacao, hardwoods including mahogany, ebony and lignum vitae, a curare vine and a kapok tree. A cacao tree more than sixty years old, moved from the earlier conservatory, still fruits, and a Canary Island date palm planted when the dome opened now approaches 70 feet (about 21 m). Nearly a hundred birds and fish live in the tropical and desert domes.

The Desert Dome sets the Sonoran Desert beside Africa (aloes, crassulas, euphorbias, Welwitschia) and Madagascar, whose collection of more than 125 specimens was dedicated in 1984. The Show Dome changes five times a year: a model railway in winter, bulbs in spring, a summer show, chrysanthemums in autumn, a tradition going back more than 120 years, and a holiday display.

The domes form the centrepiece of Milwaukee's Mitchell Park. A full visit moves through the three climates, desert and rainforest, before the Show Dome. That dome closes for about two weeks between displays, which is worth checking before a trip. In winter, from January to March, it hosts a model railway with 600 feet (about 180 m) of track among more than 4,000 plants. The Cyril Colnik gates, a relic of the 1898 conservatory, can be seen in the Show Dome.