Watering your Bonsai

***EMERGENCY***
I have a Serissa and one day I found it had completely brown foliage, although my soil was moist, as was the moss. I am constantly watering the plant now to keep it alive, can you give me any tips at all to revive my tree?

I don't know what kind of bonsai plant I have but its the kind that you buy on the side of the road 6"-8" tall.
It has this problem: the needles are turning brown and falling off. It sits on the window seal on the west side of the house. Is this a watering issue?
Please help.
Thanx (Jeans daughter),
Carissa

I've been told that immersion of the Bonsai pot in a sink full of water for an hour or more is a good thing to do. I'm concerned that this might cause excessive leaching of nutrients from the soil. I'd appreciate any comments.

regards

Lon Heath