Arum seedlings

[olegKon]

Different ssp of Arum italicum grow here (zone3) outside provided they are protected (mulched) and covered with snow. Seedlings can sometimes be hardier than adult bulbs.
As for the aroid hardiness list I would be rather careful. Min. temperature can be indicated for a short period of time (not for a 5-6 month winter we have) or for dry conditions etc. I've lost some arisaemas as I believed the list and left them outside for winter. Winters differ.

[Paul T]

Oleg's qualification is definitely true.  You have to experiment with your own areas.  The hardiness list is just examples or where things have survived.  It can often give you a hint that something might survive that otherwise would not have.  So much of course comes down to the genetic material you have as well.... some strains of a plant have adapted to warmer areas while other strains have adapted to colder areas.  Growing from seed helps, but it can sometimes depend where that seed came from in the first place as to how much cold/warm it will take.

[Robert G]

Oleg, I suspect you and I gave similiar conditions. Here we can have  -30c for a week without snow cover, a week of rain, or -5c with a lot of snow. Last year was normal, but we increasingly seem to have unstable winters. Always some cold -30c.
Paul and Oleg, you are both right about the list. Winter wet and snowless extreme cold, etc.... Too many factors.

[Sinchets]

What we also should not forget is that the world's climate has never been 'stable' and some of these plants have been around a long long time. Some plants, from areas which are warm now, may have experienced weather patterns we wouldn't deem 'normal' for those areas now.  You just have to give them a try. 

[Paul T]

And remember, the plants themselves don't read the books so they don't necessarily "know" that they're supposed to not grow in your climate.  A lot of my plants survive because I have heartlessly kept them illiterate, so they don't know that they aren't supposed to grow in my climate (my Beaugainvillea which is in full flower at present, as an example).  I never let me plants near my reference books, just in case they find out that they shouldn't be growing here in Canberra. 

[Sinchets]

Good point too, Paul. Another thing to keep plants away from are references to their distribution in the wild- or they may realise they aren't suppose to be found in the wild in a particular location. I think this is perticularly important for all those plants that are found within metres of the Bulgarian borders with Romania, Serbia, Macedonia, Greece and/ or Turkey- but not actually in Bulgaria.