Container gardens are great for decks, patios and areas where poor soil would make it all but impossible to grow a garden otherwise. However, most people choose to grow annuals in containers because they do not have to overwinter them. Plants that would normally be cold-hearty in the ground are more vulnerable to extremes in temperatures in containers, because the containers can't keep the cold away from the plant's roots as well as the soil in the ground. However, overwintering a container isn't as difficult as you think.
Group the containers that you are trying to overwinter by their characteristics. These characteristics include whether the plant goes dormant in winter, it's weather heartiness zone and the type of container that it is planted in.
Leave plants alone if they are tolerant to temperatures at least one heartiness zone below your own, are planted in heavy containers that aren't subject to repeated heating and thawing, and if the plants go dormant in the winter.
Erect a burlap wind screen around hearty evergreen plants such as boxwood or English ivy.
Store plants that are borderline on the heartiness zone, those that are in containers that are prone to freezing, and woody vines, trees and shrubs in an unheated garage or shed. Keep the soil in these containers barely moist. In the spring, when new growth appears, you can move these plants outdoors again.
Place trees, shrubs and miniature roses in a garbage bag filled with straw or dead leaves for added protection. Store these plants away from sunlight so as to not trigger early blooming.
Place each container on a bed of straw if you do not have a shed or garage. Wrap each container in newspaper and cover them with another bed of straw. Allow straw to settle between each container. Then cover with a tarp to keep rain, wind and snow off of the containers.
Dig holes in the ground if you have the space. Place the containers into the ground and then cover with a layer of mulch.
Bring tender evergreen plants such as rosemary and tropical plants indoors for the winter.
Cut back tuberous plants. Dig up the tubers and store in a paper bag filled with peat moss. Place the bag in a cool, dark place such as a closet or basement.