There are two (2) "types" of roots those that function in water & those that fuction in soil. When you see the first sign of a "root bud" then transfer to soil.
I would apply 0.3% IBA (Rooting hormone) stick in well drained soil & mist expect rooting to take 30 to 80 days

I would pot them in soil now. The roots will be much better established when you are reardy to plant out. Al

Thanks for your help.

Krissie

One thing to watch for with Persian Shield - when I propagate cuttings in the late summer and then overwinter them in my hoop house, they shift into flowering mode. Sounds like a good thing but it isn't. When inspired to flower the plants don't put on the large leaves with lots of purple, they develop shorter leaves with only a faint silver pattern and they barely put on any size. They get locked into this breeding stage for most of the following year which pretty much ruins them as flashy potted plants. I believe the short days of winter influence this but I don't have room inside my house to store them.