Please correct me if I've erred, but I believe that John Pasternak sent the bouquet of tulips in Season 3, Episode 6, Claire Underwood, who herself asks the same question as that in the question title above. The posts in this IMDB.com thread don't appear conclusive.
In Season 3, Episode 6, a bouquet of tulips were bestowed on Claire Underwood by the husband of Michael Corrigan (characterised by actor Christian Carmargo), the imprisoned gay rights activist who had earlier committed suicide in his cell (while Claire was sleeping, after she chose to remain with him). Claire then asks an assistant:
'How did he know that I like tulips'? I also wish to know; so I relay her question here.