"David E. Ross" writes:

I want to try to root cuttings of a rose from someone else's garden
(with permission), a rose that is no longer available commercially.

The question is: what type of cutting is most likely to be successful --
succulent new growth, somewhat woody but green almost mature growth, or
truly mature growth?

Green? You said _root_ cuttings. Why would the roots be green?

Aren't most rose bushes grafts? The root might not match the plant.

I have to confess, never tried a root cutting but now I know
how I can get a Rose of Sharon with unique colors into my yard.
Up until now, I've just been transplanting volunteers and hoping
for the best.

Google says, pencil thin section of root or larger.

--
Dan Espen