2 or 3 lb mini mull will slam a blunt end /12" rebar right through the rootball and pot bottom.
Many big box home improvement stores have smaller precut rebar, 2,3 or 4ft. Get a few and try them out. When you see it works great you can order the total number needed from a concrete or contractor supply house custom cut to desired length.
There is a specialized tool for cutting rebar, it's a mini electric/hydraulic shear, they are relatively safe, the jaws move slow, with a smaller opening. I've seen inexpensive units from Vevor.
It's a shame your on the other side of the continent, I've got a pile of bar, a bender and the bar snapper sitting here.