Very nice. Saturation and focus are perfect IMHO.
You got there by:
1. Masking out the leaf and/or cutting it out and putting in on another layer
2. Using the remaining material (i.e. the background) in a bw mode. You could do this any number of ways. My guess is that you used the channel mixer because doing just an Image>Adjustment>Desatuate would not produce the crispness and contrast of the final image.
Also IMHO, you used a hard-edged brush rather than a soft one for the leaf cutout. You may or may not have used dodge and burn techniques to further enhance the background. It is entirely possible that you did...and to excellent results.
Bottom line, keep up the good work and welcome to
RTP.
Janet