KUSA - It doesn't take a greenhouse to keep tropical patio plants inside during the winter.
I don't have one, and I manage to cram hundreds of plants inside to save them from the cold. It's well worth the effort, since these plants grow bigger and better each year. It doesn't make sense to start from scratch each spring.
Any bright window will do. Don't fuss and feed them all winter. Your plants need a quiet rest period. Some will cease flowering and drop leaves, but that's nothing to worry about. Bougainvilleas, for example, are notorious for often dropping every leaf. Don't worry. As long as you continue to water throughout the winter, they'll leaf out again as soon as we days start to lengthen again after the winter solstice.
Bulbous plants, such as cannas, dahlias and gladiolus, can be allowed to frost. Cut the foliage back after a freeze and store the bulbs in a cool, dark place during winter. Throw a bit of water on them once in awhile to keep them from shriveling up.
It's a good idea to keep your potted plants only slightly moist. I water thoroughly about every two weeks, but it depends on how warm your house you keep your house.
Don't worry about saving true annual plants that complete their life cycles in a single season. This includes petunias, marigolds, cosmos and impatiens. Enjoy them while they last. In protected areas (as well as covering with sheets on cold nights), they may linger for many weeks. In the meantime, add autumn color to your patio with bright mums, asters, kale, pansies and dianthus. Add pumpkins, gourds and cornstalks to complete the fall picture.