Keeping outdoor plants alive in the winter can be hard, especially if those plants are tropical or subtropical and you live in an area that has occasional freezes. In order to protect the plants, you will need some sort of additional heat during frost and freeze events. Damage due to cold weather may be limited to the foliage, or may cause serious problems to the vascular system. If that system is disrupted too much, the inability to deliver nutrients to the rest of the plant's cells could be fatal.
Plant those plants most susceptible to the cold closest to the home. If they are in a container, move them onto a screened or unheated porch. It is especially important to plant them near the south-facing side of the home.
Watch the weather forecast to determine what you need to do. In zones that are borderline for cold-susceptible plants, the forecasts will often be quite specific, focusing on how many hours are expected to be below freezing and specific locations where that is likely to occur.
Cover plants that cannot be moved indoors with sheets or blankets if temperatures approach a critical point. If they are in containers, move them closer to each other. Providing these simple protections can help prevent heat loss and keep plants and roots above the critical freezing point for longer periods of time.
Use dirt mounds around those plants that are planted in the ground. The mound should be at least 6 inches tall and 12 inches in diameter. This can provide a suitable insulation to protect trunks and roots, two of the most critical components in any plant.
Place lights on or near the plants underneath the coverings to provide further protection. An incandescent flood lamp, or even a string of Christmas lights, can be used to provide heat.
The use of heaters works best if there is little wind and the plants can be put closer together. This is also one of the most expensive options.
Use water on fruit trees during a freeze if none of these other steps is practical. Though this may seem counterintuitive, the water actually gives off heat during the change from a liquid to a solid state, which can be beneficial.