A colorful flower decoration display at the Bundesgartenschau, or BUGA, in Mannheim, Germany. The display was in the U-Halle, a former warehouse at what used to be the U.S. Army’s Spinelli Barracks.

Iconic national flowers include the Belgian red poppy, known for its association with Flanders and the losses of the First World War, the Dutch tulip and the Irish shamrock, linked to its national ...