Plants with a variety of underground food storage organs are often lumped under the heading of summer-flowering bulbs. True bulbs such as lilies, eucomis and tigridia as well as tubers (such as dahlias and caladiums), rhizomes (like cannas), and corms (that produce gladioli) all fall into the category.
Some tolerate our cold winters, but more often they are not hardy and are treated as annuals or are dug and stored each fall.
For best selection, purchase summer-blooming bulbs, corms, tubers, and rhizomes early in the spring and plant after the chance of freezing has passed. They’re available through catalogues, garden centers and nurseries. Choose bulbs that are large, firm and free of defects.
Caladiums are grown for their foliage which can be white, pink, red or green. These plants do best in shady areas or containers and prefer a highly organic, moist growing medium. After a killing frost, dig up these tubers and store them in a cool, dry place until next spring.
Cannas provide a lush, almost tropical look to flower borders, and are available in many colors and heights. For best results, plant these rhizomes six inches deep and at least 18 inches apart. After a killing frost, dig up the rhizomes and store them in vermiculite or peat moss in a cool, dry, ventilated place until the following spring.
Dahlias are a long-lasting flower with showy blooms that range in color and size to fit most cutting gardens. Plant dahlias after the last spring frost. In autumn, allow the tubers to remain in the ground for two weeks after a killing frost so they can thoroughly mature before you dig them up. Dig carefully so that the roots do not break apart. Wash the tubers and let them dry. Then pack them in vermiculite or sawdust, and store in a cool, dry place until spring.
Gladioli are available in many colors and perform well in Colorado. For best results, plant these corms three to six inches deep after the danger of frost has passed. When the tops die back in the autumn, dig, clean, and sort the corms for storage.
Asiatic lilies are typically winter hardy to zone 3 or 4. Oriental lilies and trumpet lilies prefer slightly warmer winters but are said to survive to in zone 4 if heavily mulched during the winter months. These bulbs can be planted and left in the ground.
For “Commonly Used Plant Terms” refer to message number 2008.
For more information, see the following Colorado State University Extension fact sheet(s).