Hello,
some extra suggestions :
- Nerium oleander 'Sister Agnes’ is said to be both frost hardy and vigorous. White single flowers.
- Nerium oleander 'Hardy White' - is it the same as 'Sister Agnes'? Not sure.
- Nerium oleander 'Hardy Yellow' - well, not much info about that one, but I assume flowers are yellow and it is reliably hardy

Note : all parts of Oleanders are poisonous, take care.
Note 2 : here in Italy we have many more hardy selection, but I'm not sure they would be available in the U.S.
Note 3 : Anyway, most selections are hardy to at least -8°C. Many are hardy to -10°C. Some are hardy to -12°C.
Regards, Etto.
[ Edited by Etto on 2005/10/9 10:40 ]