I'm a bit confused as to which plant you mean - Cordyline australis is the Australian Cabbage Palm, also known as Torbay Palm, but the term 'floribunda' applies to roses. Can you please clarify.

I must say, from other things you mention, that it sounds as if you have cordylines, they have flowered, the flowers have now died off and probably dropping, and the lower leaves are brown and drooping downwards. If its just the lower leaves, and there's healthy new growth at the top, this is just natural leaf loss. As they're in pots, its possible they don't have enough root room by now, which would significantly restrict their growth, and make it difficult to keep up with watering, so its possible you're losing more leaves because of that.

It might be possible to provide further information if you can add a photo or 2.

I grew some more cordylines from the seeds, when ripe I put some in pots and left them to over winter in the cold gh, they are doing verywell, must have about a dozen spread about the garden

I've just noticed you say you're feeding them with Miracle Gro - recommend you stop that straight away. They only need a top dressing of fertiiser in the spring, no other feeding is necessary, and feeding at this end of the growing season isn't a good idea in particular - believe it or not, the growing season is starting to close down, readying for the approach of autumn/winter.