I whizz them through my food processor. It can take a bit of whizzing, because my food processor is over 30yo and the blade is not as sharp as it used to be. But I end up with powder.

Ditto here. Foor processor or Vita-Mix (the champions of blenders). Just make sure the material is very dry before pulverizing (or you can end up with a pulpy mess).
Enjoy! Lynn

depends how much your doing, pestle and mortar are traditional but they are incredibly hard work (trust me) a coffee grinder may be a good idea
unlike a blender it is specifically designed for powdering, hint, make sure its clean and not full of coffee, using a spice grinder for peper my dad ended up with cinamon flavour on his dinner (i had used it for cinnamon several months beforehand)

Mrs. Kitchen, very similar to the Magic Bullet does an excellent job of powdering herbs. It is much more efficient than any coffee grinder i have used. It is also so good for smoothies! Diana

what about one of thos blender coffee grinder deelies
we have one that would work on harder bits of herb like roots i think
just a thought

How am I going to powder camote tops?

Generally speaking, let leaf material dry and then grind. Roots, twigs, or other hard when dry stuff, cut into smallish pieces before drying and grind when dry. Unless something is very unusual, this is how you do it.

FataMorgana