[Yorky]

I've had a go for the first time at the above but I've had some problems. I planted some seeds in a seed tray and some in small pots. They all grew well and fast until I transplanted the seed tray ones into pots to grow on before planting out. I followed the instructions with regard to keeping them indoors and putting them outside for a few hours each day to acclimatize bur, as I say, the transplanted ones have all died. I haven't planted any out yet and intend putting them in grow bags.
I put some polystyrene packaging in the bottom of the pots first for drainage and used peat free bark compost. When I was emptying the pots out today the polystyrene seemed to have rotted away and there was an awful smell from it. Should I have used polystyrene in this way or has it perhaps poisoned the plants? Any other theories as to why the plants might have died?

Thanks in advance.

[cooler]