Acer Palmatum Mikawa Yatsabusa

I bought a very small acer mikawa yatsabusa (about 4 ins high) about 3 years ago. I had it in a pot for 2 years & it didnt grow very well, so last year I transferred into the garden, in a well sheltered shady spot, but it just put on a few leaves & then shed them early. It seems to be doing the same this year. It seems to be not growing any at all, it is still the same height as it was 3 years ago. Is it a slow grower?. I have quite a few other different acers of varying ages both in pots & in the garden & they are all doing very well. Does this one need special attention?
PS.I have given it the odd weak solution of ericaceous plant food.
Thanks