On a few occasions (in both Buffy and Angel), a personality disorder test is mentioned and one of the questions to determine one’s sanity is if the subject ever wanted to be a florist. Additionally, whether you like shrubs or not seems to help determine your career aptitude, while a flower shop is a cover for the government conspiracy for which Riley Finn works.

Answering questions on their career aptitude tests during career week at school:
Xander: “Is murder always a crime?”
Buffy: “Do I like shrubs?”
Xander: “That’s between you and your god.”
Buffy: “(to Willow) What’d you put?”
Willow: “I came down on the side of shrubs.” - What’s My Line? (Part One)

Buffy: “The Watcher Council shrink is heavy into tests. He’s got tests for everything, T.A.T.s, Rorschach, associative logic. He even has that test to see if you’re crazy that asks if you ever hear voices or you ever wanted to be a florist.”
Willow: “Ooo, I used to want… Wait. Florist means crazy, right? I never wanted to do that.” - Doppelgängland

Buffy (on phone): “No, no, Finn is his last name. Yeah. Well, did he used to work there and then he got transferred Oh, is this actually a flower shop, or is this one of those things where I’m supposed to play along to show that I know it’s really secret ops? Oh, maybe I shouldn’t have said that. Oh, OK, right. Well, if some guy named Finn shows up to buy flowers — Yeah. Thanks.” (hangs up, turns to Spike) “Wrong number. Or a giant government conspiracy, one or the — Spike?” - The Killer in Me

Fred: “Don’t y’all think this is some kind of government conspiracy? ‘Cause my friend, Levon, says the government’s always taking kids and experimentin’ on ‘em. Did anybody else have to take a personality disorder test recently? They ask you about politics and your bowel movements and if you want to be a florist…“ - Angel, ‘Spin The Bottle’.