Here in the Sonoran Desert of Arizona we have a lot of these Cacti. They can handle the drought and heat far better than I can, alas the summer is almost over.  Some may be tired of images that reflect the never ending F/64 style, if not,  I will add my general “how-to” notes on the post of the dailyphotogame.com site. If you are well versed in digital photography then the notes will not be a surprise.  When making a back and white I always eventually get the color image in Photoshop. The order of my recipe is as follows, with variations only a cook can be blamed for.   First  Image  Adjustment  Highlight Shadow makes the image worse but adds details in both ends.  (my default settings  H18 24 18  &  S18 24 18,)  I use this regularly on all color images too, but either way the end points will need to be selected again, to bring the correct tonal range back in line.  You have to make the image ugly before it gets better with added detail! Then a new B&W layer is added on top or the background. This could be one of the RGB Channels using  Image  Apply Image or with a program like Nik Silver Effects pro, (structure and clarity).  I might use luminosity as a layer mode or one of the others, this is the area I really play with.  Like painting b&w layer through with a mask and then doing another B&W layer set to normal or using the Photoshop layer Black and White, (color sliders for more tonal change), to finish it.   Last but not least vignetting,  dodge and burn (curves), sharpening and a final check of end points using Curves to make sure they are set right for the subject, or for my taste of “more cowbell”.