I am currently living in the California Bay Area, a subtropic region. I grow quite a few tropical trees in my backyard. This winter has been the first subtropic winter that these trees have ever experienced. Typically, the nights here were 40-50 fahrenheit and days were 70 fahrenheit. There was only one night that dropped to 39 fahrenheit. I've only been watering my trees sparingly once a week because I heard trees don't need much water in the winter. None of my tropical trees appear healthy now, so I would like to assess whether they have survived the cold weather or not. Are they dead or not?
This is my Wax Apple. In the summer, it branched vigorously and had tons of huge leaves, bigger than the size of a human hand. It has dropped nearly every leaf. Also, the small outer branches have blackened. The inner bigger trunk is still tan colored. (I strung up a lot of the branches because during one storm the winds bent the branches straight down).
This is my Century Guava. It hasn't lost many leaves. However, they've become a pale yellow-green color and then eventually purple. Its branches appear unchanged - they have a flaky skin as most tropical guava have. (I know mulch isn't supposed to touch the trunk. During the dry times, I keep the mulch as close to, but not touching, the trunk).
Update on April 25, 2015
The wax apple is presumed dead. All leaves were lost during the winter. All my other tropical trees have came back from hibernation except the wax apple. I cut into its trunk to test for any green color. Nope. It was dried to the bone. Farewell, my good friend. I will need to start from ground zero again...