I doubt there is much long term adaptation. The plant either has the ability to survive, or it does not. Yes, it needs to be in sync with the seasons. So if you move it from a greenhouse into the outdoors, then yes it has to adapt. But a species won't learn to adapt to tougher winters just by experiencing gradually tougher winters. Yes, a tree can become more durable by getting larger and healthier. But this type of Lamarckian evolution is marginal, if it exists at all.
A plant keeps the seasons by using a chemical reaction that goes around in cycles, and that cycle lasts a year. So if that reaction has to oscillate more strongly (for example because it now has colder winters), the oscillation it made the previous year will have an effect on how strongly it oscillates this current year. But this type of memory kind of goes away. The plant doesn't remember past weather as far as I know. But it isn't completely disconnected from it either. But it is one way in which a plant may have to adapt. It has the genetics to keep track of the seasons. But it needs the input of the seasons for those mechanics to spring into action. And if these seasonal inputs have been absent or minor, the machinery that protects a tree during winter may activate poorly. That that could possibly have effects for several years.
Yes, there can be some epigenetic changes that occur when a plant and it's recent ancestors have experienced harsh winters. For example, the anti-freeze proteins might be over-expressed when compared to the maples back in (southern) Japan because of changes in the chromatin that build up during previous response to cold weather. But as far as we know that is quite marginal, and a subject of study currently. This is not something you can actively use.
Yes, it could be that a maple seedling grown from seeds harvested in a colder area will produce more cold-resistant offspring. But that could be because of genetic predisposition as much as through epigenetic ones. Surely, there is genetic variation among the wild populations. And that is the result of evolution that has occurred for maybe millions of years (depending on how far back the common ancestor of all Japanese maples lived.
