I live in the tri-valley. I have dwarf cavendish planted up against my house and they die to the ground every year, but come back each year if multched. They will never fruit under these conditions. They don't like frost, nor cold weather, especially cold wet weather. Even my dwarf cavendish plants I had in pots protected from frost under my patio, showed signs of dislike and cold-burn when it got down into the 30's. My recommendations are to build warm shelter, or dig them up and store them where they can go dormant.

Do they need to go dormant? I have a dwarf in a pot outside- I'd planned to bring him in when it gets cold and hang a circline bulb above 'im like I do with my tropical passifloras. They like it and sometimes even flower.

Simply hauling the pots into your garage and providing cheap wattage compact fluorescent light would keep them dormant. Do not water as often, only one cup every two weeks per pot during the winter. If they don't fit, keep them in slanted position, or trim the leaves. Take them out when the minimum temperature consistently stay above 45 deg F.

When it gets cold in the garage, hovering near the freezing temp, in case you don't have insulation, turn off the light completely and hold off on the watering.

mine was fine last winter. was growing like a weed. lol