Posted: 19/12/2013 at 17:39
I think I see what you're saying, Bob - do you mean that the soil heats up during the day and then stays warm, like a storage radiator? In which case yes, I suppose there may be some benefit from clustering pots when there are significant fluctuations in temperature between day and night.The soil can radiate heat if the sun has provided it during the day (although not if it's constantly cold).
But I'd imagine that to make the most of this effect, you'd need to un-cluster the pots when the sun is shining, to allow the pots' surfaces to absorb the sun's warmth and heat up the soil. If they do get really cold, they'll take longer to thaw out if they're clustered together, won't they?