Pflanzenschauhäuser of the Grugapark

The botanical garden is the original cell of the Grugapark. Opened on 24 May 1927, it was laid out between October 1927 and June 1929 by about a thousand unemployed workers, under the landscape architect Johannes Gabriel and garden director Rudolf Korte. It served as a teaching and experimental facility, studying among other things how plants withstand the industrial pollution of the Ruhr; species that thrived were called smoke-hardy. The first great Ruhr horticultural exhibition (Gruga) opened on 29 June 1929; the park was later reborn for the Reichsgartenschau of 1938, then for the Gruga of 1952 after wartime destruction, and for the Federal Garden Show of 1965.

In 1985 the garden's old display houses were replaced by three glass pyramids devoted to tropical rainforest, cloud forest and succulents. Sources give 1985, although a 2019 city press release speaks of a building about thirty years old, so the exact date is not unanimous. The botanical garden was formally incorporated into the Grugapark in the 1980s.

After more than thirty years of service the houses showed damage. Work began in 2019, at first conceived as a roof replacement, then widened into a full renovation lasting about two and a half years: concrete repairs in the basements, new heating, new climate control and a new roof. The total cost was about 5 million euros, of which 3 million came from the city and 2 million from the regional KInvFöG NRW programme. The pyramids reopened on 1 December 2021.

The complex consists of three glass pyramids that the sources describe as transparent; their dimensions are not published and the author of the 1985 design is not named in the documents consulted. Each pyramid corresponds to a climate: humid tropical rainforest, cloud forest and arid zone.

The original roofs were made of acrylic-glass panels. The renovation replaced them with a system of foil membrane cushions, lightweight and highly transparent to light and easier to clean; the city cites the giant glasshouse in Cornwall and Munich's Allianz Arena as precedents. The works also demanded extensive concrete repairs in the basements, more complex than expected, a new heating system and renewed climate-control and automation technology, which noticeably reduces energy costs.

The rainforest gathers useful plants, carnivorous plants and orchids, with specimens such as the traveller's palm. The succulent house presents cacti and plants of arid regions of Africa, the Americas, Madagascar and the Canary Islands. The cloud forest, where humidity is highest, shows the vegetation of the wettest regions on Earth, including tree ferns.

In the inner courtyard, a Japanese bonsai garden is described as rare in this form in Germany. A neighbouring Mediterranean house, which was not part of the works, reopened in spring 2022. The circuit also serves as a teaching tool, letting visitors feel through climate the effects of global warming.

The pyramids stand in the botanical garden, inside the Grugapark, which covers about 65 hectares. Seeing the three houses and the bonsai garden takes about an hour, and much longer if the park is explored. The Mediterranean house opens in spring only, because of the weather.

The glasshouses offer a refuge in poor weather. The park itself has the Margarethensee, the rose garden and the alpine garden, and the Ronald McDonald House designed by Friedensreich Hundertwasser stands alongside.