Significance of offering yellow roses and lilies to a woman during medieval times?

That’s not a superstition I’m familiar with, but it has the distinct ring of Victorian-era medieval fantasy rather than historical Medieval practice.

Not that there weren’t ways to “influence” the sex of your offspring, if you’re a Medieval woman. One of the more common was to hang a bag of herbs and animal bones around one’s neck. If you’re a Medieval man, you might turn your head toward the sun while thinking strong, virile thoughts at the moment of climax to plant a son.

I have a dim recollection that at some period of chivalric or romantic tradition, sending a bouquet of yellow roses meant you were breaking up with someone.

Lilies…I don’t know, but back then, if someone had sent me lilies, I might think they were looking forward to my funeral.

I’ve read similar ideas to what you spoke of. There are so many variations. One suggestion- the book entitled: The Secret Life of Flowers. It is known on booksellers offerings and libraries. That would be my first stop on your quest. This might help with bibliographical info-
https://en.m.wikipedia.org/wiki/Language_of_flowers
A lot of eras were ‘big’ on this subject. Eleanor of Aquitaine and her varied influence would be my first guess. Try ‘Courtly Love’ as a subject. Medieval superstitions and beliefs as another.
Good luck!

Well, courtly love and chivalry had nothing to do with having sex or children with the object of your adoration so it sounds like something got lost in translation there.

I would tend to agree w @Seek that it’s more the stuff of Victorian fantasies. According to this article from Pro-Flowers, yellow roses were not cultivated until after their discovery in the 18th century.

Yellow roses mean “remember”.
I wonder if Spock ever sent some to McCoy…

Texas lore has both a yellow rose(song) and a Jersey Lily