My thoughts were that if the 35mm lens was to be purchased just for flowers, then there would be better alternatives.
Before I bought the 35mm lens, I had the 17-40, 50 1.8 and 70-200 F4. I was quite new to digital photography and thought that I needed to "cover a wide range of focal lengths". In the end I tended to use the long end of the 17-40 about 50% of the time, the 50 1.8 about 40% of the time, and the occasionally the 70-200. I loved the creativity allowed by the 1.8F lens, but also liked the "feel" of the more substantial 17-40. I also felt that the 50mm focal length was slight too long (on a crop camera), so I traded all of my 3 lenses in for the 35mm. I used this as my only lens for almost a year, and loved the results. On a crop sensor I use it to take portraits (but not too close up, as there is a slight distortion effect of making closer objects such a the nose look slightly exagerated), landscapes, weddings (as a friend of the B&G, not the pro), and everything in between. I still love using it today as I did when I first got it.
To answer your question, flowers and portraits are possibly not the best subjects for this lens, it will do it, but there will be better individual alternatives. Have you considered the 50mm as you have a full frame camera?