And the moral is...

Either/or:- 
I hate the idea - use Grow-bags.
OR 
An annual soil swap, &/or or the 3rd option - I buy a load of muck. No likey just on the concept of a whole load for such a relatively small need.

It befell thusly:-
Both Jerra and I had, earlier this  year, discussed our mediocre tomato plants.  In days of yore Mam & Dad had a system.
Spring - top 2" of greenhouse soil was "swapped", tomatoes were planted, tomatoes received a 2" mulch of muck, (or Farmyard manure to the posh) as the tomatoes came out the potted Chysanths filled the greenhouse over winter and until the Daffies had "gone over" as that was where they stood during summer.
And thus she paid the rent.
I'll not delve into loam stacks & the annual chrysanth re-pot.
Anyway it appears the toms are greedy wee blighters - SO - next year I'll change sides.
What you see before you is the single, volunteer, tomato plant which grew took over the "empty side" of the greenhouse, leaned over, took root again and continued as, apparently, TWO HUGE plants, without even watering while we were doing the N. Coast 500.
A fearsome beastie is it not?