Answer: In my experience it is better to plant Cryptomeria in the spring in colder areas such as where you live. I would suggest waiting until spring to both purchase and plant. It is a bit late in the fall to plant, so it will not have time to become well rooted before winter. This will make it extra susceptible to drying out and suffering winter damage. And, it is difficult to hold a container grown plant under home conditions and keep it healthy through the winter.
If you feel you must purchase it now, plant it and keep the soil evenly moist until it freezes, then be sure to mulch generously over the root area in late fall. Also provide it with a wind break this winter. Finally, be sure to plant it in a sheltered location with good protection from winter winds to reduce the chance of winter damage in general.
Q&A Library Searching Tips