In by garden only A. palmatum which has not got any damage when -28 Celsius (~-23F) is Osakazuki. Neither A. japonicum Aconitifolium got any damage. I have read some A. triflorums are fine up to -40C (-40F) and that both A. sieboldii and A. pseudosieboldianum are hardier than palmatums. My Blodgood lost all which was above the snow but it got some bright February sun too and it broke the bark on south side which bropably was deadly.

Even on plain palmatums some thinnest autumn grown twigs die but they grow so fast that their winter preparation is not finished yet started when first freezes gome. That is problem with many Asian Maples in Finland where I live above 60 decrees latitude.

I get some autumn colors only on Osakazuki, Aconitifolium and one no name green dissectum and triflorum and all of them are hardiest. First time this fall I try to force some of my maples to prepare better. I have installed sheet of plastic on the ground around the trunk. This should reduce the water intake which is one factor of autumn colors ie winter hardiness.

Almost any of them are okay. That's my conclusion. After much discussion here and experimentation with Acer Palmatums and Acer Japonicums in my yard the past couple of years it seems that the proof is in the planting which after last year's cold, icy conditions did not affect any except by way of being reduced by a desperate rabbit who could not get to their ususal forage because the ground was frozen for three weeks.

You can follow many of the discussions we've already had on this topic, but anything I've planted in northern Illinois which does get zone 5a temps at times (but coldest lately -15 degrees) has not been affected.

One guy in Chicago south of here, with the handle Dansgarden, pretty much has planted all sorts of less common cultivars too numerous to list here (five years running). My list so far (much less time than his trees) not including the more common ones: AP Nuresagi, AJ Aconitifolium, AP Ki-Hachijo, AP Red Emperor, AP Crimson Queen, AP Hogyoku, AP Red Dragon, AP Seiryu, AS Aureum. AP Villa Taranto survived the cold but not the predators. (By the way, an update on the other trees reduced by rabbits--except for the smallest ones they all came back with new growth and surprisingly are nearly as full as before).

Actually, this year's unusual late frost in April following a warm March in the south killed off many trees, but up here the colder conditions in March and April actually did not affect the trees. Almost anyone will tell you that knows these trees that a late frost after the leaves come out in Spring can be the most destructive to these trees as many found out first hand this year.

Other than that I think the burden of proof is now on the other foot: that is instead of saying which trees (here I'm only including Japanese Maples) are okay in zone 5, it should now be which trees are not good in zone 5. I think the only one I've heard not good in zone 5 is the AP Sango kaku, sensistive to the cold winds) and perhaps AP Katsura due to early leafing).

I agree everything EZ said is true... although the caviat must be that you should expect some winter die back if the weather is cold enough...and many JM's are prone to fall burst of energy which is a hazard to the tree... I think the idea of limiting water in fall is a good one but that is not always possible with rainy falls ;>). with that caviat of potential die back ...and some using some sense to not plant them in an open prairie ( a protected area) most will grow in zone 5 ... but as EZ said do remember this past 50 year hot spell and then 10 that freeze really decimated JM's of anyone from lets say the south parts of 5b/ north parts of 6a and below. As well as some micro climate folks.It was a bizzaro experience where the "safe" JM areas were hurt and the borderline areas spared...it could be reversed in the future and in fact probably more likely to happen up there...then all bets are off ... unless you are like me and have started containerizing many of my newer trees out of paranoia. David

In my above post it should have said 10 DAY freeze...but that not all as the the game show guys say ...we then had 2-3" of heavy rain sitting on top of solidly frozen earth for several days so any tree that wasn't bark damaged on limbs was root and /or trunk damaged so whatever re-leafed out was DOOMED. It was for this area a triumvirate of distruction that wreaked havok on many but the hardiest of cultivars ... David