in the past I have used a John Innes no 3 type soil also mixed that with multipurpose compost. they grew fine for a couple of years but I lost them in the harsh winters of 2010/11/12. the pots were large and watering was the main issue with them as they were in a sunny but windy spot.

I would use the same as SBG with JI no. 2 or 3 mixed with a multipurpose. Firstly, they will be OK for a while in a pot but bare in mind that they will become a large trees given time. Also as SBG lost her plant during a cold winter, you need to shelter yours. Greens are the most hardy and the further you go down South the warmer the winters but I understand that you have milder winters in the northwest from the northeast.