We have a wonder old Australian tree fern that has at least six heads on it

Hello peterduggan

I've never encountered a multi-headed Dicksonia before ; but (and sounds very drastic) , you could cut the top completely off (!) through the trunk , obviously below where the branching occurs , *****
Plants imported into the UK from Australia and NZ have been treated as such .
They are often cut completely straight off , top and bottom , and given the correct cultivation (liberal spraying) , they always recover .

***** Growers sometimes forget that the 'trunk' is actually a tightly packed mass of roots , and is very resilient .

Go on , be brave , go for it !!

Regards
PaulB3 (UK)

PS If you do follow the above advice , try removing all fronds from cut-off heads , separate and clean up .

Plant singly in pots (your option) or in ground ; keep moist and don't be at all surprised if all of them grow !

Your next generation of D.antarctica !

Thank you so much for your advice, I will consider my options. I'd hate to kill my old mate it's a magnificent Tree fern.
Pete