Posted: 02/01/2017 at 22:24
It's a nice idea but does it have to be a pot? Most plants prefer to be in the ground, especially if they are to grow to any size as they can then spread their roots to get all the water and nutrients they need. Plants in containers are entirely dependent on you for food and water. Also, plants in containers are more likely to have their roots damaged by freezing temps unless you can take them under cover for winter.
First of all I advise you to start watching Beechgrove Garden when it starts broadcasting again in March or April on BBC 2 Scotland, repeated Sunday mornings on national BBC2. It is based at a garden near Aberdeen so has plants that should survive in your garden. You will learn all sorts about what, when, how and where with plants, planting, pruning etc.
The programme publishes fact sheets online for each programme and the website has info on the various gardens and their plants within the plot so you can check what will survive your winters and see if you'd like to give them a try - http://www.beechgrove.co.uk/ornamental-gardens
If you do choose a shrub or tree, you should know that the smaller specimens usually grow away faster and stronger than the larger ones which can take a while to get their roots established well. Roots drive upper growth and health so getting the planting conditions right.