Obsessions? Let’s just say that as a child, Mr. Groff would type out, from memory, scripts of “I Love Lucy” episodes (he also read books about Lucille Ball, a memoir by Desi Arnaz and a book about their company).

“I am a total nerd, and this role is actually closer to who I am as a person than the other parts that I’ve played on Broadway,” Mr. Groff said. “I have a whole side of me that isn’t the projected image,” he added. “I get this — I totally get it — and it feels like a natural fit.”

His physical transformation from hunky to homely has turned out to be surprisingly persuasive, so much so that this production has interpolated a recurring sight gag about the character’s unattractiveness that, by combining absurdity with plausibility, slays the audience (pardon the pun) over and over.

Mr. Groff, dressed by costume designer Tom Broecker in ill-fitting khakis and a vintage blue shirt, appears to cave in on himself during the first act of the show, as if he doesn’t even deserve to stand fully upright. He wears black mad scientist glasses, a beige cap and blue Chuck Taylors, and manages to look boxier and younger than he is in real life.

“The only way he’s not a Seymour is because he’s gorgeous,” Ms. Blanchard said. “But even that goes away — he just seems to shrink into this dorky thing.”

But is “ Little Shop” more than a lark?

“It’s about something larger — it’s Faust,” Mr. Groff said. “It’s about greed, and how far you’ll go to get what you want.” But, he added, “the reason it ran for five years Off Broadway, and there’s a movie, and every theater in the world has done it, is because it so doesn’t take itself seriously.”

Visiting the botanical garden prompted memories for Mr. Groff, who said it reminded him of childhood trips to Longwood Gardens in his home state of Pennsylvania. “The smell!” he exulted.