Orphan Heinz DITTMER born 1913

Hello,
I'm looking for possible hints of the parents of my grandfather. His name is
Heinz DITTMER. He was born on 13. November 1913 in Hannover. Supposedly he
was an orphan and lived for a while in an orphanage. Later he was living
with a foster family on a farm in the area around Hannover. The only
document I have is his death certificate but that doesn't help much.
I would appreciate any information that could help getting me one step
further.
Thank you.

Ralf Dittmer