On the subject of cuttings, is the above a good method for trying to get
polka dot plant cuttings to take root? I keep trying with houseplant
compost and dipping the stem in rooting powder but with no success.

I'm sorry, I have no idea what a polka-dot plant is.

Apparently Hypoestes phyllostachya according to:
http://www.thegardenhelper.com/hypoestes.html

Kerry