Still, the roses are red, and pink, and white, which is handy. For the magic, what is needed is, of course, the thorns, since it's protective magic. The rose blooms still let me make it quickly and colorfully clear.
So it is in fact an advantage that I had to pull in the story timeline, back to when the roses are blooming. (Since they are still in the days of old roses, once blooming and then done.)
I think I shall have to go back and put in allusions. "Don't go past the roses" is probably easy, setting geography and sorcery at once.