I think this is just gorgeous, and also love the fact that it seems to have been painted with a purpose: I presume this was done on a page in a gardener's notebook, given the collaged bits of information about rose bush species below it and some handwritten notes, too, including what looks to me to read $4.00 a bush and "good for the house." Wouldn't it be nice to imagine a group of these were planted there and bloom on still? Super lush green watercolor and super delicate feeling pinks, petal layered atop petal.Luscious. 

10 7/8" x 8" and in beautiful antique condition. I would guess 1870s-80s or so.