When using high vigor rootstocks there is some risk of root girdling and the tree becoming root bound in the pot. You probably would want to choose the rootstock partly based on scion vigor.
low vigor scion -M 26 (example Honeycrisp)
medium vigor- M 9 (example Ashmead’s Kernel)
high vigor- M 27 (example Bramley’s)…if you can get M 27
More dwarfing rootstocks usually bear fruit earlier. They also will require less pruning longterm.
Not all rootstocks develop such that they will ever girdle in a 15 or 25 gallon pot…
these would generally be the SAME ones you have to stake to get them to stand up.
Dave most of mine are on B9 which I selected for hardiness, disease resistance and M9-type size control. I didn’t use m27 and have a few on m7 which grew tall and lanky.
Not to derail the discussion in here but i am thinking now i may grow all M9 and just try a few different varieties. I consitently read about how an mm106 will perform like a dward when restricted by a container but it doesn’t sound like that is the best idea? Perhaps the tree woupd be unhappy and likely to drop fruit and whatever else?
Jamie
I’m guessing B-9 and maybe B-10 would be choices for containers. M9 G41 G11 and so forth…not enough drought tolerance; you’d be watering pretty frequent.
Anyone have experience with G202 G935 or G222 or similar sized in a container?
Thanks blueberry. Maybe b9 and b10 and closer to an m26 then? I don’t think b9 and b10 are abailable where i stay. M26 is described as semi dwarfing.
Jamie
Hmmmm…well, I bet B-9 is available…at least before “Brexit”! (Sorry, I hadn’t noticed you were in Scotland.) I can sing “Flower of Scotland” by the way. 
b.t.w. M26 probably would do ok in half a whiskey barrel. (after all the whiskey is gone ofcourse).
For those who do grow apple trees in containers, what do you do with the pot during the winter? Does it stay outside with the pot exposed to the elements, or go into the garage with the fig trees? My curiosity comes from zone 5.
Mine stay out in the elements. But Iowa is colder, so I am not sure how to advise you.
The only rootstocks I’ve had die were M111…and they died not in the middle of winter but in a 20 degree or so night after leaf buds had broken to grow.
Antonovka, B9, B118, G30, G202, No problems down to -5 F at least…sitting out in the elements.
Thanks.
I have 2 trees on m26 that i grafted this year but haven’t got in ground space for. I was going to give them away, I’d not thought about growing them in pots. I might now give them a whirl.
Finglas, you can buy B9 in the UK here B9 - Apple Rootstock - Bare Rooted. Out of stock for this year now unfortunately but might be worth keeping in mind if you wanted some next year. They have also come up on Ebay before
Thanks blueberry. Yes brexit is big in the news over here at the moment. I am from and still reside in Scotland. We are out of the EU at the moment but there is a chance we will end up back in should be separate from the UK. Unlikely i think. Lots of history, secuirty and prosperity in the Uk for people to want to vote to separate imo…anyway thanks for the advise.
Dave8abound. Great thank you. In the past i have used walcot nursery for rootstocks and i didn’t see any available there or on the few other uk sites i had tried but i will check your link out. Thank you!
Jamie
Jamie, in terms of your original question, I have heard concerns for potential root rot in oversized containers. Make sure you have drilled plenty of holes in bottom of barrel. Best of luck and have a Happy New Year!
Thanks Quill. I’m still undecided about planting straight to a large barrel or potting up along the way. I already have the whiskey barrels (i should have investigated this before hand) but it would mean setting them aside in a smallish garden but we shall see. As you you say, plenty of drainage holes and maybe a lot of grit in the soil mix?
Best wishes and happy new year too
Jamie
you could put a tree in a smaller pot inside the whiskey barrel as you progress through potting up. that would actually be nice for the tree in the summer to keep the pot out of direct sun and keep temps down