How to get rid of forgotten git branches?

Question

git

My repository traces the history shown below

Branches without a continuation have no name, git branch -athey are not visible on command. I would like to get rid of such branches in the remote repository. How can I do this if I only know the commit hash?

Answer 1

I would start with

git fetch origin
git remote prune origin

then I would go to that remote through the shell and do git gc there (although, usually, it should be done there itself)