Hi Bob and All
With reference to growing plants in 2 pots, I actually use this method myself, purely to keep the roots cool in the summer months, there is no compost in between the pots so it is nothing like growing plants on a Âring cultureÂ method (something that is frowned upon in the exhibitors world), this is merely a larger pot (in the case of the photograph an 8 inch pot) with the plant ÂInsulindeÂ growing inside this in a 7inch pot. I must say the reason that the pot is on the stand is simply to provide stability, it is a cheap and simple pot stand.
Insulinde grew this way throughout the season and I will post some more pictures to show this.
I see no reason why the space between the pots should not have some form of filler to insulate the roots and keep them cool as I said with regards to growing fuchsias in hot climates if gravel or pea shingle was used this could be watered to keep the roots cool. Perhaps even perlite or vermiculite could be used if a plant stand was employed as this would give the stability at the expense of the weight.
Anyway it provides as little food for thought