University of Vermont Extension 
Department of Plant and Soil Science

Fall News Article
Dr. Leonard Perry, Extension Professor
University of Vermont
Dahlias.  Cannas.  Gladioli.  These are the most common summer-flowering perennials that grow from bulbs or other storage organs, and that aren’t hardy over winter in northern climates.  Yet it's easy to overwinter these, and other cold-sensitive perennials that grow from bulbs, corms, and tubers, indoors so you can replant next spring.
These food storage organs (actually underground stems) are often just generally referred to as bulbs, although technically this refers to those elongate, pointed ones with scales such as daffodils.  Corms are the flattened ones, as with gladiolus.  Tubers are the large, irregular swollen storage organs such as with dahlias or tuberous begonias.
For cannas and tuberous begonias that you've grown in containers, the procedure is easy.  These can be stored indoors over winter in their pots.  Just check for insects or plant diseases before bringing them into the house.  Once the foliage dies back with cold and frosts, trim the plants back to just above the soil line.  Place in a cool but non-freezing (a cool cellar or garage, 40 to 55 degrees is ideal), dry place with good air circulation.  Most basements, particularly if heated, are too warm.  Just leave pots there until early spring, but mark your calendar so you don’t forget about them, as I did this year. 
For these plants in the garden, start by cutting back the foliage to a few inches above ground after it is frosted and turns black. Then, with a spade or other digging tool, carefully loosen the soil around each plant about six to eight inches from the crown of the plant.  Dig deep enough to get below the plant, taking care not to cut or otherwise cause a wound as this may expose the plant to infection. If you accidentally cut the plant's tubers, allow it to dry out so a scab will form before putting it in winter storage.  Store cool and dry, such as in dry peat moss, sand, sawdust, or vermiculite.
Some prepare tuberous begonias for wintering and dormancy by reducing watering and stopping fertilizer in late summer to early fall.  Removing any flowers in early fall helps the plant put energy into the roots, not more flowers. Then, when leaves turn yellow or are frosted, cut the stems about 4 to 5 inches above the tuber.  Allow plants to dry indoors for a few days until the stems are loose and easily pull off.  Remove roots and some soil, but don’t wash the tubers.
Gladiolus, crocosmia (hardy to zone 5, colder with reliable snow cover), summer hyacinth (Galtonia), cluster lilies (Brodiaea), flame freesia (Tritonia), wand flower (Sparaxis), and acidanthera are handled similarly, only they can be left in the garden later into the fall, such as late October or early November for gladiolus, but before freezing for flame freesia.  Dig plants, cut the mostly browned tops off just above the corm or bulb, and remove some roots and soil.  For gladiolus, remove and discard the old, shriveled corm. Store the wand flower and cluster lilies warm (65 to 75 degrees), the others cooler. Use a dry material, as used with tubers.
Place corms, tubers, or bulbs in a paper or mesh bag (as you sometimes get with onions or potatoes at the store).  Do not use plastic bags.  Moisture will build up inside the bag, causing rot.  Then store cool and dry, making sure to keep from freezing.  If you have more than one type of summer bulb, make sure to label bags (or pots if left in these) if you want to keep track of each separately.
Dahlias, foxtail lily (Eremurus), and crimson flag (Schizostylis) are stored slightly different, as they must be kept very slightly moist or they will shrivel and dry out.  But keep them from being too damp, or they will rot.  They are dug as other bulbs, right when the frost blackens the leaves.  Cut the stems off, remove soil from the tubers, and allow to dry or “cure” in a warm, dry place for a day.  Don’t leave longer, or they will shrivel.   
Then store tubers or bulbs in very slightly damp peat moss, sawdust, vermiculite or similar, making sure it is not wet.  You can use pots, burlap, onion bags, or similar storage material that allows some air.  As with corms, they’ll rot in plastic bags, unless bags are perforated with many holes (but then the storage material often leaks out).  Once cured, I like to pot them into fairly dry potting soil so they are ready to begin growth indoors next spring.  Then store cool, dry, and non-freezing.
Some less common bulbs, treated similar to dahlias, are the poppy anemone, Aztec lily (Sprekelia), Mexican shellflower (Tigridia), calla lilies (Zantedeschia), gloriosa lily, belladonna lily (Amaryllis), and Zephyr lily (Zephyranthes).  Keep all but the first three warmer (50 to 60 degrees).  These all can be stored in dry sand, peat moss, or vermiculite. 
Popular in gardens for a tropical effect, and often just grown as annuals, are the elephant ears (Colocasia, Alocasia) and caladiums. If you have these in pots, or in the garden and transplant into pots for winter indoors, remove all but the top couple of leaves.  Keep on the dry side over winter as they are semi-dormant, and in bright and cool (45 to 60 degrees).
If you want to store elephant ear corms or caladium tubers, dig as you would dahlias when tops are just frosted, or yellowed and mostly died.  Cure for a day, then store cool and in a dry substance.  A few elephant ear cultivars (cultivated varieties) such as ‘Black Magic’ don’t form tubers, so should be kept over winter growing in pots. 
There are several less common, often tropical, summer-flowering plants from bulbs that you may grow outdoors in pots in northern climates, and that should be brought indoors before frost.  Allow plants of achimenes to dry out, and store the “rhizome” roots dry and cool (55 to 65 degrees).  Store Nerine lily bulbs either bare or in pots, dry and cold but not freezing.  Keep plants slightly moist for pineapple lily (Eucomis), blue African lily (Agapanthus) and Peruvian lily (Alstroemeria), which can be stored cold but not freezing.  Store crinum lily bulbs similarly, or keep in containers in a bright and cool site.
Keep pots of spider lily (Hymenocallis) bright and cool, or store their bulbs dry at these temperatures.  Bring tuberose pots indoors, and keep cool and bright until blooming; then allow plants to dry and go dormant.  Veltheimia, a relative of the hyacinth, can be grown in pots in bright and cool conditions, often blooming in winter. 

Return to Perry's Perennial Pages, Articles uvmext logo