Tropical Plant Dome, Niigata Prefectural Botanical Garden (熱帯植物ドーム)

Niigata Prefectural Botanical Garden opened in December 1998 in Akiha ward, Niigata City. It was funded through a national grant for areas that host power-generation facilities (電源立地地域対策交付金). The site, of about 19.8 hectares, now holds more than 100,000 plants; it is run by a group of designated managers made up of the educational group 国際総合学園 and the prefecture's urban greening centre (新潟県都市緑化センター).

The tropical plant dome, which opened with the garden in 1998, is its centrepiece. After some twenty years of use, ageing facilities led to the first large-scale renovation since opening, completed in 2020. The works were also used to refresh the displays: about fifty more species were introduced, bringing the dome's collection to around 600, with an emphasis on tropical and subtropical plants rarely seen in Japan and on plants useful to people. A mural depicting the transition from Niigata's urban districts to its rural and mountain landscapes was added at the same time.

The tropical plant dome is a cupola 42 metres in diameter rising to 30 metres, dimensions that place it among the largest dome-shaped greenhouses in Japan. Its height allows palms of about 20 metres to grow inside, the equivalent of a five-storey building. In 2020 the structure underwent its first major programme of works since opening, prompted by the ageing of its facilities.

The garden has other indoor spaces. An exhibition hall, the 'stage of flowers and greenery' (花と緑のステージ), hosts eight exhibitions a year around a water garden displaying a wide range of aquatic plants. An atrium (花と緑のアトリウム) is set aside for seasonal displays and for presenting research. The garden also offers an aquarium area devoted to aquatic ecosystems and a space for themed displays, for example on carnivorous plants.

The dome holds about 4,000 plants of some 550 species according to the garden; an article published after the 2020 renovation gives about 600 species. Tall palms grow alongside the giant Victoria water lily (オオオニバス) with its huge leaves, and tropical fruit trees such as cacao, banana and star fruit. The renovation added useful plants including coffee, as well as a young Emmenopterys henryi, described as a first for a Japanese botanical garden.

Every year from March to May the jade vine (ヒスイカズラ, Strongylodon macrobotrys) opens its jade-coloured flowers. Outdoors, the garden keeps other notable collections: a rhododendron garden described as the largest in Japan, more than 500 horticultural and wild camellias, over 1,000 peonies of 150 varieties, about 200 species of perennials suited to Niigata's climate and a garden devoted to the prefecture's rare flora.

The garden lies in Kanazu, in Niigata's Akiha ward. The dome takes about an hour to see, but half a day allows time for the outdoor gardens as well, which cover nearly 20 hectares. Spring is a rewarding season: the jade vine flowers from March to May and the azaleas from April to June, while camellias take over from November to April. The exhibition hall changes its theme eight times a year, and hand-drawn maps, updated monthly, are available at the information centre.