My friend and fellow Japanese maple enthusiast Elisabeth Witt has been encouraging me to post information about growing them in Zone 5. The following is based on my own experience and is not purported to be scientific fact. My opinion is that the zone information on some cultivars is not entirely accurate. I have a collection of 540 different cultivars and well over 600 trees, most of them thriving, but after years of replacing certain cultivars after winter dieback I’ve come to the conclusion that there are simply some cultivars sold as appropriate for Zone 5 that are not really sufficiently hardy to be labeled as such. Let me begin by saying that in my location on the border of Northern Illinois and Southern Wisconsin winters can be particularly brutal, so what I say may not be the case for everyone, but if you are located in Zone 5a and your winters are harsh, you may want to avoid cultivars with which I’ve personally experienced repeated failure. Sango kaku, Orange Dream, and Mikawa yatsubusa annually have a complete branch die all the way back to the trunk (that survives to send out new branches the following year.) Other very popular cultivars that lack winter hardiness in extreme conditions are Shin Deshojo, Shishigashira, and Kamagata. Almost all the colored bark cultivars are susceptible to significant winter dieback. I was very sad to lose the beautiful Radiant TM that had been provided me by David Freed who introduced it and asked me to test it. A few cultivars that I believe may be more recent introductions that have failed to thrive are: Kawahara Rose, Giganteum, Tendoh, Koyasan, Kawahara midori (numerous attempts,) Shirofu nikishi, Koshibori nikishi, and Murehibari. Let me be clear that I am not suggesting dishonesty on anyone’s part. Nurseries are going on the information provided them. I think the people who actually assign the Zone ratings simply don’t know how cultivars will respond to the extremes within any particular zone. I suspect this is true to some extent for the warmer zones as well as the cold.