Posted: 03/02/2016 at 06:24
I use John Innes No 3 soil based compost with several handfuls of horticultural grit added for my bay. They're not really happy in multi-purpose compost.
They're also greedy feeders when in pots and need several doses of fertiliser throughout the growing period. I also spray the leaves of mine with seaweed spray about once every couple of weeks. That perks them up no end.
I suggest that you should re-pot your tree in March, using loam-based John Innes No 3 with added grit, and an appropriate sized pot.
One of the additional benefits of using the loam-based compost is that it is much heavier than MPC (multi-purpose compost) and so even if your tree is in a smaller pot it will be weighted down and shouldn't be top heavy and blow over.
There's an explanation of over-potting and problems caused here https://www.rhs.org.uk/advice/profile?PID=864