We went to the Arboretum the week after their tulip festival. This border was one of just a few tulip plantings that was still pretty enough to enjoy. For the life of me, I don’t know what the black is across the top of this photo. We were not there in the dark.
Pretty shot- yes as others have said your dof and the difference in light is what darkened your background. Isn't it amazing how our eyes automatically adjust that for us? A camera can't do that though- hence what you did not see in reality shows up in your photo.