very rarely, almost never
“My sister lives in Australia, so I only get to see her once in a blue moon.”
“I don’t know why I bought that CD-ROM for my computer – I only ever use it once in a blue moon.”
Have you seen their house lately? It’s really gone to the dogs.
It’s true that it has become run-down and in serious need of repair, but I’m sure that it can be fixed up to look like new.
I guess with a little carpentry work and some paint it could look pretty decent.