Oh lord, are you saying there was no drainage in the pot? Not good, do it as soon as possible. Also I'd like to know if you're keeping it under shelter or inside - this is a very hardy plant and will do perfectly well out in the open, though where you live, I guess there was a strong possibility it might have frozen solid this year! And I'd just mention that you will need a larger pot fairly soon anyway.

although its a slow grower, this plant will be a massive outdoor plant one day, i have seen them with a girth of 20ft standing 80ft high, beautiful specimens.
It looks to me like over water or water logging is the problem, get yourself a larger pot, fill with soil and free draining compost and sit back and admire it.