I was hunting for the same info after finishing the last chapter! From what I've dug up, 'Rose Thorns' stands alone as a complete story for now. The author, Celia Vane, wrapped up the main narrative arcs pretty definitively—the protagonist's quest for her family's lost heirloom concluded, and the romantic tension with the rival botanist got a clear resolution. I haven't seen any announcements about a direct sequel. It seems like the writer moved on to a new series, 'Whisperwood', which is a different setting entirely. Maybe check her website for any bonus epilogue content? I remember she posted a short, non-canon holiday scene once, but that's about it. Honestly, I'm a bit bummed. The world felt rich enough to explore further, with the whole magical botany guild system. I keep hoping she'll circle back to it someday, but no signs yet.
That said, if you're craving something with a similar vibe, 'The Glasshouse Alchemist' by another author has that mix of historical fantasy and thorny plant magic. It doesn't have the same characters, obviously, but it scratches a similar itch for me. I reread 'Rose Thorns' every couple of years and just imagine what happened to the side characters after the last page.