TBH, hard as glass doesn't appeal to me personally for drawing. I like a nice, soft charcoal so it doesn't scratch paper and makes bolder lines and flow... But awesome regardless of my useless opinion!

What kind of surface is it better with?

Oh this is so cool. I never thought about making your own drawing charcoal with plants.

I have a huge retort for making fuel for my forge, but if you're just making small batches you can use a paint can or an altoids tin even, there are lots of easy plans online about it. Artists have been making their own for a long time.

Neat! I used to draw with charcoal, but I haven’t done anything more than doodle for like a decade. Maybe combining it with my love of gardening and plants will help bring back that spark?