As we approach the latter part of September, the inevitable task of having to put your summer blooming bulbs to rest is sure to be on your mind. Flowers such as Dahlias, Cannas, Gladiolas, Caladiums, Colocasias and Alocasias are not hardy in Wisconsin and therefore are considered “tender bulbs”. We can still enjoy these wonderful plants with just a little more effort at the end of the summer in order to ensure their survival.
Types of Fleshy Underground Roots: True bulbs are actually made up of scales or rings which are modified leaves. Most of the tender summer “bulbs” we grow here in Wisconsin, aren’t actually bulbs at all. They are corms, tubers or rhizomes, all fleshy, underground roots. For our discussion here, we’re going to simplify things and just call them bulbs.
Dahlias: In our area, USDA Zone 5, light frost can help Dahlia bulbs go dormant. About a week before a killing frost occurs, the foliage should be cut back to 1-2 inches above the ground. Dig the bulbs and gently shake the soil from them. If any of the bulbs are rotten, carefully cut these off. The bulbs are fragile, so handle with care.
Leave the bulbs upside down to dry naturally for a couple of days. Keep them from direct sunlight. Once dry, remove any remaining soil and pack them in slightly moistened sawdust, vermiculite, peat moss or sand. Store the bulbs in a well-ventilated, frost-free place with the temperature between 35 and 50 degrees F, with 40-45 degrees F being ideal. Check them periodically over the winter to make sure they are not rotting or drying out. Remove any rotted bulbs to preventing spreading of disease and mist any that appear withered.
Cannas: Cannas should be dug after frost has caused the foliage to blacken and die back. The bulb itself shouldn’t freeze, so make sure you don’t leave these in the ground too long. Once the bulbs are dug, wash all of the soil from them. Do not scour or scrub the bulb as this will cause wounds or scratches on it, giving disease and insect pests a place to attack. After washing, cut the foliage back to 2-3” and allow the bulbs to dry for a couple of days. Once dry, the bulbs can be placed in paper bags or newspaper. Store in a dark, cool place for winter. A storage temperature of 45-65 degrees F is ideal. As with Dahlias, check them periodically over winter for disease and desiccation.
Gladiolas: Once Gladiolas are done blooming, they concentrate all of their energy into the bulb. That’s why it’s important to wait to dig Gladiolas until all of the foliage has turned brown and died back. Once this has happened, generally about eight weeks after flowering, it’s safe to dig the bulbs. Dig the bulbs up and allow them to sit on the soil surface and dry for 2 approximately days.
After they have dried for two days, place them in a cardboard box. Place the box in a warm (85 degrees F) location, with good air circulation for about two weeks. This allows them to dry completely and for the new bulbs, which have formed on top of the old bulbs, to separate from the old. There may also be “bulblets” or baby bulbs that have formed. After separation, remove the excess dirt, cut back the foliage and place the new bulbs and bulblets in the box and discard the old bulbs.
Store the bulbs in single layers in a cardboard box, in a mesh bag or paper sacks. Storage temperature should be 35-55 degrees F, with 40-45 degrees F being ideal.
Caladiums: In the fall, allow your Caladiums to die back naturally. The leaves should dry up and fall off. Carefully dig the bulbs before the first frost and place them in a warm, dry location for a couple of weeks to dry out. Lay them out on paper towel or newspaper and provide good air circulation over them. Turn them during drying to ensure that all sides are thoroughly drying.
Remove the foliage by cutting it off close to the bulb. Be careful not to cut into the bulb because this increases the chances for disease or insect pests to move in during storage. Place the bulbs in a mesh bag, box or open flats to ensure good ventilation. Cover in dry peat moss and store in a dry location. Caladium bulbs should be stored at a temperature of 65 degrees or above.
Colocasia/Alocasia: The foliage of Colocasia/Alocasia should be allowed to remain on the plant, until the leaves turn yellow in the fall. Similar to Gladiolas, the green leaves continue to store energy to feed the bulbs for growth the following year. Allow the first frost to kill the top growth. Cut the foliage down to 2 inches and dig the bulbs. Allow them to dry for a day or two in the shade. Remove all of the foliage and then place the bulbs in a box filled with dry, course sawdust or peat moss. Store the box in an area where the temperature is between 55 and 65 degrees F. When cutting the foliage, you may want to wear gloves, as the leaves contain oxalic acid, which may cause irritation to exposed skin.
For those people who enjoy these majestic plants, a little extra care will help you to enjoy these summer favorites year after year. If you have specific questions about any of these tender bulbs or others, please feel free to contact us.