I thought bamboos were supposed to be tough as old nails?? Overwatered? dunno. Grasses should be good - especially the really tall ones.
I've got a cordyline in a pot and Alan Titchmarsh recommended wrapping it up in fleece each winter, which I did for the first few years. I don't bother now its more established, but it's fairly mild here.
how much sun have you got? I've got a fantastic castor oil plant in a humongous pot which I bought quite tiny in August last year and it's grown like topsy. I've watered it once and it doesn't get any direct sun at all. Will have to water it in summer I guess...