Extension News

Spice up Your Garden with Tender Summer Blooming Bulbs, Corms and Tubers

Note to media editors: This is the ISU Extension Garden Column for the week of June 13, 2008.


Summer blooming bulbs are long-blooming and have showy flowers available in a wide range of colors. None of the following perennials will survive our cold Iowa winters. Therefore, they must be dug in the fall and stored indoors through the winter months. All should be planted in spring after the frost threat has passed and the soil temperatures are above 60 degrees F. This usually means planting in mid to late May at the earliest.

Tuberous Begonias (Begonia x tuberhybrida) do best in protected sites in partial shade. They are available in upright and trailing types. Flowers may be single or double and are available in a variety of colors and forms. Flower forms available include camellia, rose and carnation. Height ranges from 8 inches to almost 2 feet with the majority staying within 8 - 12 inches.


Plant the disk-shaped tubers 2-3 inches deep with the round side down. Keep the plants well-watered and fertilize them regularly for continuous bloom. These beauties work well in containers and can be brought indoors in the fall for winter enjoyment.


Those tuberous begonias left outdoors should be carefully dug after a killing frost. Dry the tubers in a warm, dry location for approximately 2 weeks. Afterwards, bury the tubers in sphagnum moss or vermiculite in a box or sack and store in a cool, dry location until spring.

Gladiolus (Gladiolus hybrids) are unequaled for their cheery cut flowers. Glads are easy to grow and available in almost every color of the rainbow. It is generally safe to begin planting glads in early to mid-April in Iowa. 


Successive plantings can be made every 2 to 3 weeks for continuous bloom from mid-summer to frost.  The final planting should be made in early July. Corms should be planted 4-6 inches deep and 5-inches apart.


Glads prefer a sunny location with well-drained soil. Plant heights vary from 2 to 3 feet for miniature varieties and 3 to 6 feet for the standard varieties. Tall varieties often require staking for extra support. Carefully dig up the glads when the foliage yellows or after the first hard freeze in the fall. Cut off the foliage 1 to 2 inches above the corms and allow the corms to dry for 1 to 2 weeks.


After drying (curing), remove and discard the dried remains of the old corm located at the bottom of the large, healthy corm. Place the corms in a mesh bag or old nylon stocking and store in a dry, cool, frost-free area until replanting in spring.

The torch-like blooms and large, banana-like foliage of the Canna (Canna x generalis) make a bold statement in summer gardens. Some varieties are giants reaching up to 8 feet tall. Use these garden giants as temporary screens or hedges.


Dwarf forms reaching only 2-3 feet tall are also available. Flower colors include apricot, orange, red, white, pink, yellow, variegated and speckled. Foliage color also ranges from bright green to variegated with combinations of yellow, maroon, red, bronze, cream and green.

Cannas thrive in the summer heat and prefer full sun and a rich, moist or wet soil. They should be fertilized periodically for continuous blooms throughout the summer. Rhizomes should be planted 4-6 inches deep.


Dig the rhizomes after the foliage has been blackened by frost. Store the cannas in slightly moist sand or vermiculite in a well ventilated, cool, frost-free location until planting in spring.

Dahlias (Dahlia x hybrida) stand out like beacons in the summer garden. There are over ten thousand cultivated varieties of dahlias with every color represented except brown and true blue. With eighteen different flower forms ranging from pompons to cactus, it would be hard for someone not to like at least one type.


The blooms range in size from one to seventeen inches across! Plant heights vary from two feet for bedding dahlias to twenty feet for giant tree dahlias. Blooming begins around the end of July and continues until frost.

Dahlias should be planted six inches deep. Rows should be spaced about one and a half feet apart. The taller dahlias will require staking, as they cannot support themselves. As the plants develop, buds appear in the center of the dahlia. At this time, one of two things can be done at this time.


The first option is to remove the center bud. This procedure is known as topping to encourage lateral (side) bud development. The other option, called disbudding, is to remove the lateral (side) buds to maximize the size of one flower. After a killing frost has destroyed the foliage, the tubers should be carefully dug, cleaned, labeled and stored in vermiculite for the long winter months ahead.

Although many of these summer blooming bulbs require more work to store over the winter, they are well worth the effort for their colorful and unusual blooms and foliage.



Contacts :

James Romer , Horticulture, (515) 294-2336, jromer@iastate.edu

Jean McGuire , Extension Communications and Marketing, (515) 294-7033, jmcguire@iastate.edu