From this post: https://meta.stackexchange.com/questions/78048/enable-automatic-deletion-of-old-unanswered-zero-score-questions-after-a-year


> **If the question is more than `30` days old, and ...**
> 
> - has −1 or lower score
> - has no answers
> - is not locked
> 
> **...or...**
> 
> - it was closed and migrated to a different site
> 
> ... it will be automatically deleted.

**TL;DR** "Tumbleweed" Questions get automatically deleted as of May 2011