Why have the bottom leaves of my mature cordyline turned brown?
Answers:
Don't worry - it is normal for the bottom leaves to go brown.
Gently take off the brown leaves and you'll see a wonderful trunk appearing.
You only need to worry if no new leaves appear at the top.
Other answers:
Underwaterd them and too much heat
Underwaterd them and too much heat
wind burn possibly
theres been a naughty animal around that there plant...
highwinds will burn the leaves the plant grows for thirty years + you can pull off damaged brown leaves .
goodluck
various under watering, wind burn. natural growth , dog
I would say as u have the tips damaged as well that it's wind/or frost although this is a hardy plant you can still get sone damage