Acer tres

I have a couple of Acer tree in pots, couple of years old
The leaves are turning brown on some of the leaves
Its well drained and fed every few weeks
Any idea what is causing the leaves to go brown like this ?

I give them a spray with water, evening and morning

Not sure if its good for them though

Might be a problem with that, my garden has full sun (when it is shining) all day
It maybe the wind it can whip around my garden when it does blow
I dont really want to put netting or a fleece to protect it from the sun (may not have any choice)
Its hard to find a shady spot in my garden