What you say is true. Phormium cookianum ssp. cookianum occurs in the
highest altitude regions of New Zealand and would be the most tolerant of
cold. The problem is identifying the cultivars of Phormium cookianum ssp.
cookianum that are specifically the most cold hardy. Much experimental
testing for cold hardiness needs to be done. An effort should be made to
produce improved cold hardy cultivars.

There are many Phormium cultivars in the trade but most of them, especially
those of P.tenax, would not be expected to be cold hardy.

http://www.houseleeks.freeserve.co.uk/phormium.htm


Wardle, P. (1979) VARIATION IN PHORMIUM COOKIANUM (AGAVACEAE). New Zealand
Journal of Botany 17 (2): 189-196.


Pam - gardengal wrote in message
news:vKwMb.31583$sv6.96486@attbi_s52...

"Cereoid-UR12-" wrote in message
om...
Exactly where on the planet are you?

Are you trying to grow them where they normally don't survive the
winter?

Most Phormium cultivars cannot tolerate freezing temperatures.


They are reliably winter hardy to zone 8, 20F. Many of the hybrid
cultivars
(with P. cookianum parentage) are somewhat hardier, specially if drainage
is
very good. These originate from high mountainous, even alpine, areas of NZ
and can tolerate quite a lot of cold weather.

pam - gardengal