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Overwintering Containers

Overwintering Containers

By Melinda Myers for Milorganite
Photographs by Melinda Myers, LLC

Planters filled with trees, shrubs and perennials make great additions to any size landscape. They increase gardening space, bring the garden to your back door, provide screening and add beauty, fragrance and pollinator appeal to outdoor living spaces. With winter looming it is time to prepare them for the change of seasons so they remain healthy and beautiful when spring arrives.

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Container gardens need extra care for winter since the plant roots are more exposed and subject to damage from extreme cold and hot temperatures. The smaller volume of soil in a container does not provide the same insulation and water holding ability as in-ground gardens. This exposure can result in root damage and even death of plants growing in containers.

Plants that are one zone hardier than your growing region and potted in a large container usually survive with little extra care. Just water whenever the soil is thawed and dry to prevent the roots from desiccating over winter.

Make sure any container left outdoors for winter is weatherproof. Terra cotta and ceramic pots are subject to damage in areas with freezing temperatures. When water turns to ice it expands causing the pots to break. Fiberglass, resin, wood and other weatherproof materials tolerate harsh winter conditions. Plastic will survive a few winters as long as they are not bumped once frozen. By the time plastic pots need replacing your plants usually need to be moved into a larger container anyway.

Try one of these methods for container gardens that need extra winter protection:

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Place all the containers together in a sheltered location. Surround these with pots of petunias, impatiens or other annuals for added insulation. Compost those annual plants in spring after they serve one last function in the landscape. Woodchip mulch, bales of straw, bags of soil, and similar items also work. Cover with snow where available for an added layer of insulation and moisture when the temperatures rise and the snow melts.

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An unheated garage will also work in colder climates. The goal is to keep the plants dormant. Set pots on a board or old carpet and surround them with bags of shredded paper, packing materials and bags of mulch or potting soil if additional root insulation is needed. Water whenever the soil is thawed and dry. For those gardening in snowy regions, place a scoop of salt-free snow on each pot. When a winter thaw arrives the snow will melt and provide needed moisture. Dry roots, not cold temperatures, are more often the cause of death.

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Growing plants in plastic nursery pots set into a decorative container for the growing season makes overwintering much easier. Lift the potted plants out of the decorative container and bury the pot in a vacant area in the landscape. Cover the pot with soil, leave the plant stems exposed and let nature take care of the rest. After the ground freezes you can cover the plants with evergreen boughs for added insulation.

These methods also work for any trees, shrubs and perennials that did not get planted during the growing season. They will be safe for the winter and ready to move into their permanent location when the planting season arrives.

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Tropicals and other plants that are not hardy to your area will need more protection. Move these indoors if needed, grow them like a houseplant and enjoy the extra greenery. Don’t be alarmed as leaves yellow and drop. These will soon be replaced by more shade tolerant leaves suited to the indoor growing conditions. Monitor and manage pests as needed and wait until spring to fertilize.

Some like hibiscus and mandevilla can be stored in a cool location with limited light. Just water often enough to prevent the roots from drying. The key to success is finding the right location for the plants overwintered in this way.

Those lucky enough to garden outdoors year round just need to continue their container garden care regime. Adjust watering and fertilizing as needed based on the growing conditions in your area.

One last option to consider. Let winter kill, then compost non-hardy plants. Replace them with new varieties to enjoy next year. Then move hardy plants into the landscape before winter for added long-term beauty. Buy new plants for your containers next spring and enjoy your newly designed containers while expanding your planting beds.

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