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Over-wintering tender bulbs

We are a week into the fall season and experience tells us that hard frosts are not far away. With frost, the blooming life of cannas, dahlias, gladiolas, and calla lilies will come to an end. Because of their tender nature, the corms, tubers, and rhizomes (grouped together as “tender bulbs”) that produce these plants are killed by our cold winters and cannot be left in the soil. Fortunately, they can be dug and brought indoors for storage through the winter months.

When digging cannas, dahlias, and calla lilies, it is important to loosen the roots gently with a fork or spade, digging several inches back from the base of the plants so that the roots are not cut off unnecessarily. Loosen the soil on all sides of the plant before lifting the clump of roots and soil. Avoid cutting or breaking the fleshy structure as this creates an entry point for disease.

Dig dahlias after frost has damaged or killed the foliage. After digging, gently wash tubers with a hose to remove excess soil. Cure them for about three days in an area of high humidity to avoid tuber desiccation. Pack the tubers in vermiculite, sphagnum peat, sawdust, or wood shavings. Store the tubers between temperatures of 40 to 50 degrees F.

Cannas should be dug after frost has damaged the foliage. Cut the stems back to 2-3 inches after digging and wash off excess soil. Let the rhizomes dry a few days before placing them into storage. Pack rhizomes in boxes and cover with vermiculite, sphagnum peat or sand and store between temperatures of 40 to 50 degrees F.

Dig calla lilies after frost has killed the foliage or after it turns yellow. Let them cure indoors for a few days and store them in peat moss, vermiculite, sawdust or perlite. Place them in a room or basement where the temperature is kept at a range of 50 to 55 degrees F.

Gladiolus should be dug when frost kills the foliage. After digging, cut off the foliage and cure corms for two to three weeks in a dry, well-ventilated area at about 60 to 70 degrees F. After curing, remove and discard the old corm and the cormels that have formed during the summer. Cormels are miniature corms, but unless you are willing to wait two to three years to get a blooming size corm, discard them. Store in trays, labeled paper bags, mesh bags or old nylon stockings at a temperature of 35 to 40 degrees F.

Check periodically during the storage season and if needed, remove any damaged or rotting material. With a little care your prized plants should be in excellent condition for planting next spring. Source: Carl Hoffman, Extension Educator Emeritus.


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