Arboretum of Mainau, Botanical garden collection on Mainau Island, Germany.

The Arboretum of Mainau lies mostly south of the castle on the island's plateau in Lake Constance. Its tree collection holds more than 500 species of deciduous and coniferous trees, among them giant sequoias grown from seeds brought from California in 1853. Each tree is labelled with its German and scientific name and its botanical origin.

Grand Duke Frederick I of Baden, who collected rare trees from around the world, had exotic trees planted on Mainau soon after buying the island in 1853. Seeds of the giant sequoia arrived from California that year, and in 1864 he had numerous specimens planted; these are among the oldest of their kind in Europe. The collections were enlarged and tended over the following decades.

The trees are labelled with their German and scientific names and their botanical origin, so a walk through the collection works as a self-guided survey of woody plants from Asia, North America and Europe. The plantings lie mostly on the plateau south of the castle.

The arboretum lies mostly on the plateau south of the castle, so enter from the castle side and walk south. Every tree is labelled with its German and scientific name and its botanical origin, which makes the collection easy to follow on foot. A botanical guide to Mainau's flora is sold on the island.

The metasequoia, native to China, was planted in 1952 as a 70-centimetre sapling in the shore garden, making it one of the oldest of its kind in Germany. The giant sequoia seeds came from California in 1853, and Frederick I had many trees planted in 1864.