Furcraea longaeva & Arundos

Furcraea longaeva is a yucca-like plant which, on tall stems (up to 12m in the wild, but 2m here),
bears white flowers that turn into bulbils and develop into plantlets. It is a fascinating plant with a good story to sell it but it has two drawbacks; it isn’t really hardy (Z9, H3) and it doesn’t flower readily – in fact if anybody can tell me what it needs to induce flowering I would be grateful. There is a picture on www.jackdawsfield.co.uk , taken at Wisley last year, growing in containers.
In the same garden at Wisley there were Arundos in pots which is probably the best way of growing them in the garden. The species is green, Variegata is white variegated and Versicolor (as we call it) is cream variegated. All are vigorous, water-loving, grasses growing to 3m or more with broad leaves, but not generally flowering in this country. The species is a weed of waterways even in northern France so they should survive here. If the roots are under water it will of course protect them from frost.