We just had an unexpected cold wave with rain. My bougainvillea has withered up and the flowers shrank. It almost looks dried out, but I had watered the day prior to the storm. Should I prune it back now or wait until early spring? The plant is in a pot outside in a sheltered patio.
Your plant is likely suffering from over watering and or the cold, depending on how low the temps were.
Bougainvillea can endure temps to 30 degrees F., but if the soil was wet the cold can have more of an effect.
Allow the plant to dry out, make sure it has proper drainage.
You can trim away any dead or damaged material, but wait for full pruning for late winter or early spring.
Here are some links for you with more information.