I just realized it is “This Side of Paradise” instead of the other side.
This is the one where the colonists are all presumed dead because of deadly bertol rays or is it vertol rays? Anyway they are all healthy and basically living in paradise with no worries but the are accomplishing nothing.
All the crew eventually also fall prey to the spores which both protect them and also act sort of like an opiate, making them happy but not productive.
Spock finds a girl friend and is happy with her.