Sakata Seed Green House, Sagamihara Park (サカタのタネグリーンハウス)

Sagamihara Park, run by Kanagawa Prefecture, opened on 27 April 1979. In October 1992 it hosted the 9th National Urban Greening Fair held in Kanagawa and was completely redeveloped for the occasion. The manager's documents now describe a park built around a two-level flagship building, the Green House, which contains a tropical greenhouse.

A group combining the Kanagawa Park Association and the seed company Sakata Seed has managed the park since fiscal 2006, according to a 2013 business plan, and the Green House has come under a user-fee system since fiscal 2009, which leaves the manager to set the charges. Sakata Seed acquired the naming rights in April 2010, and the building became the "Sakata Seed Green House". Japanese Wikipedia mentions a first term to March 2014, then a second from April 2015 to March 2022.

A business plan published by the association in 2020 recalls that the atrium, at first a paid area, was made free in fiscal 2015 and given a café open all year, in order to draw more visitors towards the paid zones. The greenhouse is still active in 2026: in July the park's blog announced the gallery exhibitors for the second half of the year, and in September the theatre schedule for October.

The building covers 2,276 m² on the ground for 3,124 m² of floor space; the part under glass measures 1,087 m² and the ridge reaches 17 m. It is divided into two main parts: an indoor tropical garden, the Tropical Garden, designed after the tropics of South-East Asia, and an atrium, a double-height central hall. The building also holds the Green Theatre (205 m²), the main hall, the gallery, the cactus garden on the upper floor and the viewing room known as the "rainbow room". A glass-walled rest corner, the Aqua Terrace, looks outwards, and inside the tropical garden a staircase beside a waterfall climbs to a terrace covered in bougainvillea.

A 2011 photograph published on Wikimedia Commons shows a glass façade in a large grid beneath a run of gables, standing on pillars above a pond; the 2020 business plan does mention a perimeter pond, and the 2013 plan lists glass cleaning of the greenhouse four times a year and mechanically operated ventilation windows.

The heating is its most unusual feature. The greenhouse is connected to the neighbouring Sagamihara incinerator (the Minami plant): combustion heat produces pressurised hot water, sent to a heat exchanger in the building, which supplies water at about 70 °C for heating and air conditioning all year; the cooled water then returns to the plant.

The official website presents the Tropical Garden as an indoor flower garden with a different approach from that of conventional ecological greenhouses. The featured plants are chosen for their flowers: the hisuikazura, a liana from Philippine forests that is threatened with extinction, flowers from February to June; vanilla, a Mexican orchid with green-yellow flowers, from March to June; the tacca, nicknamed the "devil flower", from February to March; the dombeya, known as the "pink ball", from October to April. There are also a Vietnamese camellia with large red flowers, the jaboticaba, whose fruit grows directly on the trunk, the Philippine medinilla, a variegated banana with striped fruit and bougainvillea in flower almost all year.

Upstairs, the Cactus Garden gathers dozens of cacti and succulents, including a "kinshachi" 80 cm across, one of the largest in the prefecture, and a "curtain of light" made of more than 15,000 metal pieces. The gallery changes its flower-themed exhibitions by period, and the manager's documents mention displays of Sakata Seed's own varieties.

The greenhouse stands on the central axis of the park. Visitors approach it across the fountain plaza, flanked by two avenues of metasequoias: with the greenhouse in the middle they form a symmetrical view that the official website compares to a French garden, and the upper-floor viewing room overlooks it. A woodland path, the Komorebi no Michi, passes by the greenhouse; the Minazuki-en iris garden (2,300 m², around 120 varieties) holds its festival in June, with flowering from late May to mid-June.

The greenhouse's flowers take turns all year; late winter and spring bring together the hisuikazura, the tacca and the vanilla. The park is reached by bus from Odakyu's Sagami-Ōno station (about twenty minutes) or from JR's Hara-Tōma station (about five).