I have been in this beautiful are for a little under one year. I have a Winged Elm and Zelkova Serrata in two large pots because I have decided to go big on the trunks. They are both about 2 weeks repotted (repotted because the plastic pots they came in were absolutely in terrible condition). In southern california this winter we are experiencing strangly cold weather (32 and lower).

Since this kind of cold is not a usual occurence here in California I am a little afraid of the soil freezing. I am curious about something. I have some mulch (mostly barks and recycled tree trimming from the city mulch) can I place about an inch of this on  the top of the bonsai soil to protect the roots?

If you're mulching, don't just put it on top of the pot. Put the pot on the ground, pile mulch up over the pot to cover an inch or two of the trunk.

Plaicing mulch only on the top of the soil of a pot does not good. The heat will be lost from the sides...

@rockm: That makes perfect sense. here is the issue I am facing however. What if I cannot put the pot on the ground?

If you don't have too many, you could put the pot in a plastic bin and drop mulch in there.  Make sure to provide drainage.  Move the bin near the house.

@bigdave: l ok yeah this latest cold spell has been unusually cold so I kinda freaked out. Thank you every one