The meaning of tulips was first mentioned in Season 1 when Violet Bridgerton (Ruth Gemmell) was sitting with Anthony (Jonathan Bailey) while embroidering the flower. "This is for Daphne," Violet told her eldest son. "Tulips, they symbolize passion. A most appropriate hem for your sister when she decides to marry the Duke. Perhaps your bride would like the same."
In Season 2, tulips again came into play when Anthony visited Kate after she awakened following her horse accident. He showed up with a bouquet of tulips in hand — something that could have been foreshadowing that Kate would be the one to become his bride. Although Anthony's initial proposal (which appeared to come out of obligation in order to protect Kate's honor) was rejected, Kate ultimately said yes when he proposed again after declaring his love for her.
Another instance involving tulips can be found in Julia Quinn's The Viscount Who Loved Me, the book on which Season 2 was based. In this scene, Anthony plucked a tulip for Kate when they were out in the gardens, resulting in playful banter between the pair. Here's an excerpt from the book:
She fiddled with the flower some more, then blurted out, “You shouldn’t have picked this.”
“You should have a tulip,” he said matter-of-factly. “It isn’t right that Edwina receives all the flowers."
Kate’s stomach, already tense and prickly, did a little flip. “Nonetheless,” she managed to say, “your gardener will surely not appreciate the mutilation of his work."
He smiled devilishly. “He’ll blame one of my younger siblings.”
She couldn’t help but smile. “I should think less of you for such a ploy,” she said.
“But you don’t?”
She shook her head. “But then again, it’s not as if my opinion of you could sink very much lower.”
“Ouch.” He shook a finger at her. “I thought you were supposed to be on your best behavior.”
Kate looked around. “It doesn’t count if there is no one nearby to hear me, right?”
“I can hear you.”
“You certainly don’t count.”
His head dipped a little closer in her direction. “I should think I was the only one who did.”
