Tender Summer Blooming Bulbs, Corms, and Tubers

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. They should be carefully sorted and any damaged or diseased bulbs, corms, or tubers should be discarded prior to storage. All should be planted frost in spring after the threat of has passed and the soil temperatures are above 60 F. This usually means planting in mid to late May at the earliest.

The tuberous begonia tuber is disk-shaped. It enlarges as it grows, but does not form multiple tubers.

Tuberous Begonias (Begonia x tuberhybrida) easily brighten a shady corner of the garden. They do best in protected sites in partial shade. They are available in upright and trailing types, single or double flowers, a wide variety of vibrant colors (bi-colors) and flower forms. Some of the flower forms available include camellia, cascade, carnation, and picotee types as well as the stamina-packed non-stop series. Height ranges from 8 inches to almost 2 feet with the majority staying within 8 - 12 inches. Plant the tubers 2-3 inches deep with the round side down. To get early blooming plants, home gardeners can plant them indoors 4 to 6 weeks before setting them outdoors in the spring. Keep these 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 tubers in a warm, dry location for approximately 2 weeks. Afterwards store in a box or sack with sphagnum moss or vermiculite in a frost-free area until replanting in spring.

Caladium forms a true tuber or enlarged underground stem. New tubers grow from the side of the original one.

Another great tuber for the shade is the Fancy Leaf Caladium (Caladium x hortulanum). This plant is cherished for its foliage rather than its flowers. With its vivid foliage colors of red, pink, green, and white, it will brighten the darkest spots in the garden. Many varieties are available with contrasting leaf venation colors and patterns. Plants generally stay 12-18 inches tall. Caladium prefers a shaded site with moist soil and protection from strong winds. Plant tubers 2-3 inches deep when the soil temperature reaches 60 F. Place the tubers round side up. When the foliage dies in the fall, gently lift the tubers and dry them for a couple of weeks. Store the tubers in dry sand, vermiculite, or sphagnum moss in a cool, frost-free area.

Gladiolus corms form immediately above the old corm.

Gladiolus (Gladiolus hybrids) are unequaled for their cheery cut flowers. Glads are easy to grow and available in almost every color of the rainbow. If you stagger corm plantings 2-3 weeks apart from late spring to mid-summer, you will be rewarded with continuous blooms from mid-summer to frost. Corms should be planted 4-6 inches deep and 5-inches apart. Plant sizes vary from 2-3 feet for miniature varieties and 3-6 feet for the standard varieties. Glads prefer a sunny spot with well-drained soil. Tall varieties often require staking for extra support. After the foliage yellows carefully lift the corms, remove the foliage, and allow to dry for a week in the sun. Lightly dust the corms with a fungicide to prevent disease and cure at 80-85 F for 2 more weeks. Remove and discard the dried remains of the old corm located at the bottom of the large, healthy corm. Store the corms in a dry, cool, frost-free area until replanting in spring.

For something more tropical looking try a few Calla Lilies (Zantedeschia spp.) in the garden. From the Greek word meaning "beautiful", the elegant calla certainly lives up to its name. These unusual trumpet-shaped blooms (correctly termed spathes) prefer full sun to partial shade in moist or wet soils rich with organic matter. They make great border plants for water gardens. Fertilize regularly for best flowering. Plant size varies from 12-24 inches depending on species. Flower colors include yellow, pink, cream, white, lavender, peach, apricot, and salmon. The mottled foliage is also attractive. Plant the rhizomes 3-4 inches deep with a 12-18 inch spacing between plants. After the foliage has darkened in fall, dig and store the rhizomes in dry sand or vermiculite in a cool, frost-free area.

Often mistaken for Allium, the loose globular blooms of Agapanthus (Agapanthus spp.) work well in many garden situations. They are particularly effective in containers as patio plantings. Plant corms 2 inches deep in full sun to part shade and a moist, well-drained soil. Flower colors are predominately lilac-blue to white. Container plantings make it easy to bring the plants indoors for the winter. Given plenty of sun indoors, they will continue to bloom throughout the winter.

The torch-like blooms and large, banana-like foliage of the Canna (Canna x generalis) make a bold statement in many summer gardens. Some varieties are giants reaching up to 6 feet tall. Use these garden giants as temporary screens or hedges. Dwarf forms reaching only 2-3 feet tall are also available. Flower colors on both the giant and dwarf forms 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 regularly for continuous blooms throughout the summer. Rhizomes are planted horizontally in the ground 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.

The tuberous root of dahlia resembles a sweet potato. Note the bud located at the base of the old stem, a region often called the crown..

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 fifteen different flower forms ranging from pompons to cactus, it would be hard for someone not to like at least one variation. The blooms range in size from one to seventeen inches across! Dahlias range in height from two feet tall 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 about 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. One of two things can be done at this time. The first option is to remove the center bud. This procedure is known as tipping to encourage lateral bud development. The other option, called disbudding, is to remove the lateral buds to encourage a large center bud. 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.

This article originally appeared in the June 26, 1998 issue, pp. 87-88.