Storage of Tender Bulbs

Published: November 1, 2008

Many of the ornamental plants that adorn our landscape form storage bulbs or roots as a means of survival from one growing season to the next in their native habitat. Since many of these species are not winter hardy at our latitude these storage structures should be dug and stored soon after the tops are killed by freezing temperatures. Examples of such garden plants include (tuberous) begonia, caladium, canna, elephant ear, gladiolus, dahlia and others.

Proper storage is important to make sure these bulbs will survive the winter months and make a glorious display of color in our garden the following growing season. Temperature and moisture are two important storage conditions that influence greatly the ability to store successfully any bulb or root.

Tuberous begonias should be dug immediately after the first killing frost. Allow the tops of the plant to remain on the tubers and spread them in a warm, dry location to dry thoroughly. After about 14 days remove the tops of the plants from the tubers and store the latter in peat moss, vermiculite or sawdust that is slightly moist. Begonia tubers should be stored at temperatures between 40 and 50 degrees F.

Cannas should be cut to the ground after the tops have frozen back and before the storage tubers are dug. Turn the tubers upside down after digging and allow them to dry outdoors for several hours. This will allow cut surface to begin to heal. Next move the tubers into a well-ventilated room to dry (cure) for several more days but not to the point that the tubers begin to shrivel. Place the tubers in dry peat moss, vermiculite or sand to keep them from drying out during the winter and store in a cool location but above freezing. A temperature of 40 degrees F is considered ideal. Do not be concerned if a bit of soil adheres to the tubers; it will not be harmful unless it contains pathogens.

Dahlia roots tend to be a bit more challenging to store that other tuberous roots because they have a thin skin that causes them to dry excessively unless protected. When digging dahlia roots take care not to damage the narrow neck between the crown of the plant and the ticker storage root. Allow the roots to dry for several days in a warm, dry location that is well-ventilated. Pack them in boxes filled with moistened peat moss or vermiculite and store them at a temperature close to 40 degrees F. A single dahlia plant often forms two or more healthy storage roots in one season of growth. Unless storage conditions are ideal it is best to wait until the following spring to divide these roots.

Gladiolus should be dug and allowed to dry in a room that is warm, dry and well ventilated. The storage organ of a gladiolus is a short, thick underground portion of the stem called a “corm”. New corms form immediately above the corm planted the previous spring. After the tops have dried they can be removed from the new corm along with the old corm and any “cormels”. Clean the corms and store in open boxes or hang them in mesh bags at temperatures between 40 and 50 degrees F.

Caladium and elephant ear are tropical plants grown for their showy foliage. Since they are tropical in nature they must be stored at warmer temperatures. After digging, remove excess soil from bulbs or tubers but do not wash them. Allow them to dry in a warm, dry location with good air circulation for 7 to 10 days. After drying, pull off the foliage of the caladiums but cut off the foliage of the elephant ear about two to three inches above the bulb. Place the dried bulbs or tubers in dry peat moss or vermiculite and store at about 60 degree F.

In all cases, it is a good idea to check stored material periodically during the winter months and remove any that might be diseased. At the same time, check moisture status of the bulbs stored in moist media such as peat moss or vermiculite. As a general rule, it is better to error on the dry side rather than the wet. Excess moisture in storage can be very damaging.