Although I tend to limit my plant feeding you will need to feed a very little and often as your subjects are in containers and feed is washed away by watering and rain. Vitax Q4 has lots of trace elements but is expensive so be a little mean with it.

when I had one in a pot I used a slow release feed designed for them as instructed on the bottle.

My neighbour has an Acer nursery and shows them and she only uses liquid seaweed on hers.

Thank you all!