A pet project of his was the Buenos Aires Botanical Garden, for which he petitioned the city government to set aside land (almost 8 hectares), which he designed in sections to display plants organised by continent, with a large section devoted to the native plants of Argentina, which were ignored in garden-making at the time. The garden has the first "Ginkgo biloba" planted in Argentina. Completed in 1898, it bears his name, the "Jardín Botánico Carlos Thays de la Ciudad Autónoma de Buenos Aires". One greenhouse, was first erected at the Paris Exposition of 1889 and brought in sections from France to be reassembled, one of five in the garden. A brick house in the English Gothic Revival style, in which he lived during the construction and planting of the garden, now houses the herbarium and a small botanical library.