Erodium: Big fun, little tree, perfect for indoors or beginners!!

[ZombieNick]

I planted a bunch of these in my landscape last year, had no idea they would work as bonsai. I am still a little lost as to how to grow the "trunks", do you just expose the roots, almost like negari style?

Here is a picture of the ones I planted, labelled "Heron's Bill", anyone have any idea if these would be suitable?