In 1880, the Federazione Orticola Italiana (Italian Federation for Horticulture Sciences) organized the first National Exhibition in Florence, and authorities at the botanical garden wanted to complete the garden with a big tepidarium, the largest in Italy. Head of the project was the architect and engineer Giacomo Roster and it was built by the Officina Michelucci firm from Pistoia. In 1887, the garden was enhanced with a café and restaurant, as well as a second greenhouse, which was taken from Villa Demidoff in San Donato. In 1911, the gardens were home to another important event: celebrations for the 50th anniversary of Italian Unification. For the occasion, the garden underwent many changes, including the construction of the Loggetta Bondi, overseen by the Manifattura di Signa.
Starting around WWI, the garden and the Società Toscana d'Orticoltura (Horticulture Society of Tuscany) experienced a period of decline, and in 1930, the botanical garden was bought by the city, after which it was made public. Roster’s large tepidarium had long been abandoned, so the city restored it between 1933 and 1936. Sadly, the structure was damaged during WWII and had to be restored again after the war.