Hi AikDjogja,
Ashes are a fertilizer , in the ground no problem -the rain will wash the ashes away -, but with potted trees like in the photo, it will burn the trees - like any fertilizer if you give too much, you burn the plants.
So yes, it is time to wash the ashes from the leaves and the most of ashes from the inside of the pots.
If you can, keep the ashes in a bucket and distribute them later as a fertilizer ... :)