In regard to people it's used to describe someone who needs pampering or special conditions.
It doesn't exclusively mean high maintenance, but, needing special circumstances on some level to flourish, grow, be happy, or stable.
"He's kind of a hothouse plant. If he doesn't draw everyday he just wilts into depression."
(Nicholas Nickleby, 1838)"Mrs. Witterly is of a very excitable nature, very delicate, very fragile, a hothouse plant."
On an episode of "Frazier," Frazier was complaining about various things that bothered him. His father said, "Aren't you the little hothouse orchid."