Posted: 23/05/2013 at 18:54
With indeterminates, Bf, the larger the pot the more chance the plant has of reaching its potential. Personally, I wouldn't go under 25 litres but they'll cope in 20 litres.
Most importantly, look for pot depth. The plants will need staking and the stakes need depth of soil for stability. Too shallow and the stakes - and plants - will blow over in the first strong wind.