Posted: 09/04/2017 at 23:10
I think this tree is probably hungry and may well respond to some TLC.
This malus can, indeed, be grown in apot but it needs to be a decent sized one - min 60cms deep and wide - and filled with good John Innnes no 3 compost mixed with a bit of multi-purpose for moisture retention. Dunk your current pot in a bucket of water till no further air bubbles appear then remove the plant and use you fingers to loosen the roots and encourage them to grow outwards. Plant at the same depth as before.
It will be netirely dependent on your for food and water and will get stressed if you let it get thirsty of hungry. You'll need to give it a generous dollop of slow release fertiliser in spring and occasional liquid feeds of tomato food thru the season till mid July at the latest so any new growth has time to harden off before frosts.
Given this encouragement it should put on new growth and may well balance out but, just in case, here's an easy guide to pruning form the RHS - https://www.rhs.org.uk/advice/profile?PID=858