When I’m working in graphite, my pencil sharpener is always close at hand. But not only that, I also have a sheet of fine sandpaper upon which to sharpen the point rather than using the pencil-eating sharpener every time. You’ll find that in most of the e-booklets in my bookstore on this site I discuss these and other materials in detail.
I recommend a sharpener like the one in the illustration below. It not only sharpens traditional wooden pencils but is able to accommodate mechanical pencil graphite as well through a small opening on the side.
These simple measures ensure sharp graphite pencils for the fine detail we need to produce in botanical drawings. But you will find that different artists have different preferences for ensuring sharp pencil points. For instance, I’ve seen one artist advocate shaving away the wood and exposing at least a half inch of graphite. This too is fine, even if unnecessary and a bit tricky using a sharp blade. After all, it’s more about the sharp graphite pencils and less about how you achieve it.