Grows in almost any soil - what do you mean they keep dying? Are you not watering when there's no rain? Or do you mean you lost cordylines after this last winter? That wouldn't be surprising, a lot of people did because of the harshness of the winter.

I have three Cordylines growing successfully in my clay pit - also known as my front garden! So I agree with Bamboo, I guess they're good in anything.

cordylines will appreciate a dose of blood, fish and bone in the spring. the essentials to all large specimens is water esp in hot conditions