Tips on keeping cherry trees healthy?

pinkskyinthecity

Since I've had for 4 yo 'Sunburst", after fruiting, the leaves go yellow (and curl a little) year after year. I don't know what I can do to prevent this. With context: the tree is grown in amongst a well packed (fertilised) flower and shrub bed. 

Does any know why this is an issue? 

Thanks. 

pinkskyinthecity

Oh, I forgot to mention that the flowers have budded (looks like a bumper crop this year!) and it's leafed out beautifully.