From this post: Enable automatic deletion of old, unanswered, zero-score questions after a year?
If the question is more than
365days old, and ...
- has a score of 0 or a score of 1 with a deleted owner
- has no answers
- is not locked
- has a viewcount ≤ the age of the question in days times 1.5
- has ≤1 comments
TL;DR "Tumbleweed" Questions get automatically deleted as of May 2011