Flower bulbs are categorized into two basic groups: hardy and tender. Hardy bulbs such as tulip, daffodil, and crocus, can tolerate freezing temperatures and can require cold to break dormancy and bloom. Tender bulbs are often not true bulbs, but are rhizomes, corms, or tubers. Tender bulbs, including canna, gladiolus, dahlia, caladium and begonia, need to be dug and stored every year in order to survive.
Now that fall is approaching, it is time to think about digging the tender bulbs. Most bulbs can be left until the foliage dries or is killed by light frost. Once the foliage is killed by frost, the bulb needs to be dug within a few days to prevent microorganisms from entering the bulb at the damaged stem and causing rot.
When digging, proceed carefully to prevent damage to the structure. Loosen the roots all around the plant with a digging fork inserted several inches from the base. Lift the clump while avoiding cutting, breaking, or bruising the bulbs. Take special care with the skin of dahlia tubers. Any injured area is a pathway for pathogens to enter and cause rot during storage.
Once out of the ground, shake off excess soil and cut off the stems, with two exceptions. Both begonia and caladium should be cured with foliage intact. Plants such as cannas and dahlias are best washed with a gentle stream of water from a hose. Placing the bulbs on hardware cloth over a garbage can contains the mess and makes recycling the soil and water easier. Other bulbs are best left unwashed and the remainder of the soil removed once the bulb is dry.
Canna are dried 1–2 days and dahlia only a few hours before storage. Cleaned canna rhizomes can be wrapped in newspaper or layered in peat moss and stored in paper bags or cardboard boxes. Dahlia roots can be packed in boxes and covered with vermiculite or peat moss or placed in plastic bags with small perforations. Store both at 40–50° and check periodically to make sure they have not dried out, adding moisture if necessary.
Dry begonia and caladium bulbs 1–2 weeks, cutting back the foliage after it turns yellow. Store both in vermiculite or peat moss, and at a warmer temperature than most bulbs (50–55°).
Dry gladiolus in a warm sunny location for 1–2 days, then move them to a well- ventilated location for 3 weeks. Remove the old shriveled corms and store only the new, plump ones at 35-45° in a labeled paper bag.
The most daunting task can be finding the ideal place to store the bulbs. A location with the proper temperature, where it will not freeze and the relative humidity stays in the 50% range is ideal. Exhaust fumes in a garage can be detrimental to the bulbs, so consider instead a root cellar or an unheated portion of a basement for a storage location.
With all bulbs, discard any that are diseased and carefully inspect for insects before storage. Mark all plant material carefully, including identifying characteristics. Periodically inspect the bulbs over the winter and remove any that show signs of decay.
With a bit of care, these flowers will produce for years and are well worth the extra effort they require.
Certified Master Gardener