I don't have much experience with Firma and maybe it's symbiotic with what it is granted to. I have a IceBreaker on Firma Rootstock. IMO, while the roots of it have grown larger, it has not nearly filled in much as I would think Icebreaker is getting larger year by year, albeit very very Very Sl0wLy..... Is the slow root growth symbiotic due to the slow growth up top.
