What you do to prepare your plants for the winter will depend on what the climate is where you live and whether the temperature drops below freezing. Additional measures will need to be taken if you are living somewhere with very harsh or prolonged winters. But if you live in a region with relatively mild winters, there is very little you will need to do in order to prepare your plants.
Place portable potted plants in sunny areas during the day. If you can get your plants enough sunlight during the day and keep them warm enough at night, you might not have to resort to more drastic steps for keeping your plants alive over winter. This option is generally only available for smaller potted plants that can be readily moved without risking strain or injury.
Prune your flowers and plants to a height of 2 to 3 inches above the ground. The more exposed your flowers or plants are, the more likely they will suffer ill effects from the cold weather. Longer stems and bulbs are especially susceptible to the cold and so cutting these back will help protect the flowers and plants. If you live in an area that gets particularly cold, you can also cover the exposed portion of the flow with burlap sackcloth or plastic sheeting to help provide additional insulation.
Put down a thick layer of compost and mulch at the beginning of winter around the base of your plants. This will not only help to nourish your plants during the winter months, but will also act as insulation to keep the upper root areas of your plants warm over winter.
Move outdoor potted plants inside, especially those in stoneware pots. Planting pots, especially stoneware varieties, do little in terms of insulating the roots of your plants. If the temperatures drop below freezing, it is very unlikely that your potted plants will survive the experience. Instead, find somewhere warm inside to keep them when cold snaps are expected.
Store your potted plants for the winter and encourage them to go dormant. If you live in a particularly cold region with prolonged winters, you can move your potted plants to a cool, dark area that will remain between 40 and 50 degrees Fahrenheit throughout the winter. They will soon go dormant and can be left that way until the weather becomes sunny once more.