What I love about this image is that you’ve shown the transition from a regular sky to a more saturated and vibrant sky. This is one of the most common applications for a polarizing filter. It helps make the sky slightly more saturated with a darker, richer blue rather than a washed out light blue.
I do have a couple of suggestions about your photographs though. I’m not sure I agree with your choice of framing. Your choice of amputation of the bottom frame seems a little awkward to me. You’ve included some of the stem and cut off part of the leaf. I think including this leaf would have been beneficial. The rest of the frame is great, it’s just the bottom wall I’m concerned with.
My second concern is lighting. It appears that your main object is back lit, which is great, but you need to throw more light back on the main object to properly expose it. You could use a white piece of paper, a piece of foam core (a large sheet only costs $7) or a reflector. Reflectors are great because they roll up into a small bag and they take only seconds to unroll and roll back up. This would allow you to re-direct the light back onto your main subject.
The back lighting of a sunflower is really nice. It causes a nice highlight around the object, but exposing the texture of the sunflower seeds is also attractive. For example: