| All of the three local Cordylines will easily survive 3C - even -3C. Cordyline australis is very resiliant. Endless rain, high winds, salt spray and nibbling by stock are all part of living to a fine old age. It is known to live in both Scotland and Cornwall-Devon with few problems. C. banksii doesn't grow as tall but is also hardy in zone 9. C. indivisa is a plant of misty mountain areas and thin soils. They will grow in tubs but would probably do better in the ground. If you have been growing the varieties of C. fruticosa then IMO you'd need a very favourable microclimate outside or a glasshouse held above freezing to get them to carry through the winter. I expect my two 'rescued' 'Caruba' cordylines will be in for the cooler weather - or I'll be out scampering round on frosty nights with my billowing draperies of frost cloths! | 
