Posted: 01/01/2016 at 02:33
Hi Craigh, I have (presumably) one of the very same 'family' apple trees from T&M and grew it in a large (50cm) container for several years before it went into the ground. I used a John Innes #3 compost and it did very well without needing any extra fertiliser for the first year or two. After that I scraped-off the top inch and a half or so of compost in the container and replaced it with more JI #3, mixed with a small handful of fish, blood and bone. If keeping it in a pot for the foreseeable future, this would be the way to go I would say.
However, the best advice I can give you is to let it blossom next year and enjoy that but remove any and all developing fruit which may set in that first year after planting. This will allow the tree to establish a good root system and will pay future dividends. It is hard to resist the temptation to let it fruit while so young but it really is worth the wait! The other thing you should do is prune it properly while young. The 'essence' is that the weakest of the three grafted varieties needs pruning the hardest. This seems to go against common sense but the old adage 'growth follows the knife' is never more true than when pruning fruit trees. There is a lot of advice available if you google 'prune young apple tree' but if you are unsure about anything, post back here and someone will be more than happy to advise.
Happy New Year to you too!