Jillofalltrades, I hope you don't regret using polystyrene when you have to pick the bits out of the compost heap at some time in the future. Drives me mad!
I use crocks for all my pots, plastic or not, because it stops the soil dribbling out when I water. And obviously for drainage and to make large pots lighter....
Sorry I hadn't finished...accidentally pressed return!
I'm not sure that 40 plants constitutes a scientific study, it's a rather small control group and there seem to be lot of variables. But when I buy plants from a big nursery they don't seem to have crocks in and they grow perfectly well, so maybe there is something to it. I think I'll carry on for now and then see what happens when I run out of crocks.....(it has been known to happen).
I put crocks in my pots, because I always have. I don't think I could stop just like putting crosses on brussel sprouts before you cook them always done it lol