Posted: 26/02/2015 at 08:41
Kale (and other brassicas - other than small cabbages) don't do well in containers - they need to be firmed well in to the soil and often they need staking as well to prevent wind rock. The compost/soil in containers is never firm enough to do this effectively in my experience.
Potatoes would be better grown in bags as they need a good depth of soil - up to 3 ft, as the deeper you can earth them up the more potatoes you'll get http://www.primrose.co.uk/patio-potato-bag-p-5555.html?src=prod_col
As for carrots and beetroot, if you choose stump-rooted varieties of carrots and globe varieties of beetroot, you could grow them in a container of about 12" deep.