This postcard is part of a five card series featuring stamps of the world, ©1965. The stamps appear to be from the late 1950s to early 1960s. The Luxembourg stamp in the center commemorates a 1959 flower festival. Above and to the left of center is a British stamp commemorating the 1964 International Botanical Congress in Edinburgh.
I looked up the British stamp and found a post about that stamp and its designers: Stamps and plants make for a lasting union. The stamp shown has a "dog rose" and is part of a four stamp set that also includes Spring gentian, Honeysuckle, and Fringed Water Lily. The designers were Michael and Sylvia Goaman, who also designed other stamps featuring plants and flowers, including the Queen's 1953 Coronation stamp with floral emblems of the UK.
This is a post for Sunday Stamps at Viridian's Postcard Blog