Fall is upon us!  Frost will soon sweep its deadly, icy grip across our beloved plants that we’ve cultivated and nurtured this season.  Container plants, in particular, can be a challenge to preserve if they incorporate not just annuals, but showy tropicals, perennials, and hardy woody plants as well.  What does one do with a mixed container during the winter?  No worries!  There are many techniques for saving annual, perennial, tropical, and dry-loving container plants that will preserve them for seasons to come.

Preservation techniques will vary depending on the plants in your container. Tropical plants can be over-wintered using methods replicating a dry season, forcing the plant into dormancy; hardy perennials and woody shrubs need a cold dormancy to grow in the spring, so they must stay outside; cacti and succulents prefer their winters warm and dry and must be brought inside; while many annuals can be propagated by stem cuttings or just re-potted and maintained inside.

Tropical Bulbs/Tubers
Many tropical plants, such as cannas (Cannas spp.), elephant ears (Colocasia spp.), and angel’s trumpet (Brugmansia spp.) can be saved from an untimely death by over-wintering them in a dark corner or sunny window, depending on the type of plant. 

A lot of bulbous/tuberous tropical plants have a natural dry season (analogous to our winter) when their leafy parts die off, leaving the bulb behind.  Don’t throw them away!  After heavy frosts turn the above ground plant parts to mush, cut the damaged foliage off about four inches above the thickened bulb.  Then, dig them up and remove all excess soil from the roots. 

At this point, you can determine if the clump needs dividing.  If it needs dividing, be sure to dust all cut surfaces with a sulfur-based fungicide made for bulbs to prevent the wounds from rotting.  Cut the roots back to one inch from the bulb and leave it to dry out evenly.  Rotten bulbs/roots need to be thrown away so infection doesn’t spread to healthy bulbs.

Sitting on something absorbent like newspaper, a bulb/tuber’s drying time can last up to two weeks if located somewhere shaded and dry such as a garage or basement.  Once clean and dry, bulbs should be stored preferably around 50° F all winter in damp (not soggy) milled peat moss.  This prevents the bulbs from drying out any further, which could cause them to die.  Many gardeners don’t have a perfectly cool basement or garage to keep bulbs dormant.  Alternative methods for dry storage include a dark closet with the door cracked for circulation, a cabinet, or underneath a bed in a cardboard box punched with a few holes also for airflow.  The important thing to keep in mind is that the bulb needs to be kept on the dry side, in the dark, and moderately warm. 

If the bulbs were grown as a single specimen in their own pot, the entire pot can be placed in a garage which stays above 50° F or a cool basement and allowed to dry out completely.  Cut all above ground plant parts flush with the soil and don’t water until outside temperatures stabilize above 60° F.  Often, bulbs break dormancy unexpectedly in this dry pot method.  If this happens, pots can be moved to a sunny location near a window and watered sparingly until they can be placed outside.  The emerging leaves will be stunted, but once outside, the plant will replace any spindly leaves with lush, new ones.

Tropical Vines, Shrubs, and Trees
Tropical vines, shrubs, and trees such as jasmine (Jasminum spp.), hibiscus (Hibiscus spp.), angel’s trumpet (Brugmansia sp.), and cannas (Canna spp.) can be brought inside in preparation for next year’s display.  If frost warnings are in effect, plants need to be brought in quickly or else all plant parts may die.  In a perfect world, the ones you’d like to save should be cut back by half, sprayed for pests to prevent future pest issues, and brought in before the first frost.

Dig the desired plant out of its summer home and place in a pot with highly milled peat moss.  Most tropical plants benefit from having some sunlight in the winter, so choose an area for the tropical that has a moderate amount of light such as a living room corner or heated garage. 

Additionally, keeping the plants on the dry side helps to reduce growth and preserve dormancy until temperatures stabilize at about 60° F.  Curtail any fertilizing until spring to inhibit active growth.  Plants may lose most or all of their leaves, but as long as the stems stay green and pliable, the plants should be fine for spring planting.  Minimal conditions keep the plants alive but discourage active growth.  When outside temperatures stabilize in the 60’s, plants can be brought outside.  To avoid foliage burn, keep them in a shady area until they’ve adjusted to increased sun exposure.

Annuals
Many herbaceous annuals can also be saved for the following year.  By rooting stem cuttings in water on a sunny windowsill, plants like impatiens (Impatiens sp.), coleus (Coleus sp.), Persian shield (Strobilanthes dyerianus), Mexican petunia (Ruellia sp.), sweet potato vine (Ipomoea sp.) cultivars, and purple heart (Tradescantia sp.) can be held over winter until needed in the spring. 

Otherwise, the plants can be cut back by half, potted in a peat-based soil-less mix, and placed on a sunny windowsill.  With a wide assortment of “annuals” available in the market, some research is required to determine which annuals can be over wintered successfully.  True annuals (e.g., basils, cockscomb, zinnias, etc.)—regardless of any treatment given—will go to seed and die when brought inside.

Cacti and Succulents
If you planted a mixed dry container this year and want to retain any of the plants for next year, they should be removed from the main container and re-potted into a high sand content soil mix for cacti and succulents.  Keep them in a sunny window and water when dry.  Many succulents and cacti do well indoors, either in a heated garage or moderately sunny corner of a living room. 

As with other tropical plants, succulents also need time to adjust to sunnier conditions in the spring.  Move them to a shady spot outside when temperatures have stabilized above 60° F and then gradually introduce them to brighter conditions.

Hardy Perennials, Shrubs, and Vines
Hardy perennials, woody shrubs, and vines needn’t be thrown away when its time to get rid of accent containers.  Crack-resistant, four-season containers can house perennials and woody shrubs year round. 

• Shade perennials (Zone 4 – 7) like coral bells (Heuchera spp.), lenten rose (Helleborus spp.), assorted hardy ferns, and Japanese forest grass (Hakonechloa sp.) are great for all-weather containers. 
  
  
• Sun-loving perennials (Zone 4 – 7) such as sedges (Carex spp.), some salvias (Salvia spp.), tickseed (Coreopsis spp.), purple coneflower (Echinacea purpurea), daylily (Hemerocallis spp.), spiderwort (Tradescantia spp.), and bee blossom (Gaura spp.) are also very hardy and do well in year-round containers.  Inter-plant them with cool growing plants like kale, pansies, and Swiss chard for fall/spring interest. 
  
  
• Woody shrubs and vines—many of which have great foliage interest and some have four-season appeal—make them ideal for container gardens.  Red-twigged dogwood (Cornus sericea) cultivars (Zone 3 – 7), clematis vine (Clematis spp.) cultivars (Zone 4 – 8), and dwarf crape myrtle (Laegerstroemia spp.) cultivars (Zone 6 – 9) are great container additions that can stay outdoors year-round. 

If the container has to be removed, hardy perennials and woody shrubs can be temporarily planted in the ground and mulched.  Dig them from the garden in the spring, if you wish, and replant into a container.  Or, leave them in their garden spot and start over with fresh ideas and new plant material.

Sustainable Plants and Money in Your Pocket
Over wintering is a great form of sustainable plant conservation achieved simply and effectively by adhering to each plant’s cultural needs.  With careful planning and storage techniques, you’ll save money as well as plant material.  The beauty and interest you’ve created in this season’s well-grown container combination can also provide enjoyment for years to come.

Photos:
From top to bottom, a mixed container; container of succulents and cacti; container with vine; mixed container detail; colorful and leafy container; Ilex 'Sparkleberry' fall foliage and berries; elegant mixed container. All plants shown except for the Ilex 'Sparkleberry' are from the U.S. National Arboretum's Introduction Garden.