Question
This was the first year in So. California that we had frost on some nights and a very unusually cold winter. It has begun to warm up now but my poor bougainvillea that covers our backyard wall is bare with many dead leaves! It has many bare areas and you can see through the trellis it is attached to at top that gives us privacy from our neighbor.
What should we do??  Is it repairable??  

Answer
Tam, its difficult without seeing the damage, but from what you are saying, I'm inclined to think it may have been killed by the freeze (they are very sensitive to cold damage). Check the cambium layer (just inside the bark) and see if it still shows green; it still may be salvaged. Scratch the bark at the bottom to check it; if it is indeed green then cut the boug back to about 2 feet from the ground and it will regenerate growth ( they are very resilient plants) good luck..Nick