Since 1865, Germany has hosted an
Internationale Gartenbauausstellung (International Horticulture Exhibition) every few years. In 1953, it was in Hamburg.
Commemorative cancels were available at the event.

The stamps on your cover are a mix of normal postage from the BRD:
Top left: Mona Lisa, MiNr 148 from 15 Apr 52
2 on top row at right: second Federal Youth Plan, MiNr 153 & 154 from 17 Sep 52
Green 10 Pf middle top row: 125th Birthday of Henri Dunant, MiNr 164 from 8 May 53
Bottom row: International Stamp Exhibition, MiNr 171-172, 29 Jul 53
The five Berlin stamps in the middle row are listed as Berlin MiNr 91-95.