University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article
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SUMMER-FLOWERING BULBS
 
Dr. Leonard Perry, Extension Professor
University of Vermont
 
When you hear the word “bulbs”, the first plants that come to mind are likely the spring-flowering ones such as daffodils and tulips.  Yet there are “tender” bulbs that produce summer flowers, providing an addition to bedding plants.  They provide beauty in landscapes, are easy to grow, and can be dug and saved for replanting year after year, making them economical.  Not included in this group are the hardy perennials from bulbs, such as most lilies or bearded iris.
           
A number of different types of tender summer bulbs provide a range of colors with interesting blooms and foliage. Among my favorites are tuberous begonias, gladiolus, canna, and dahlia.  Although they’re commonly referred to as “bulbs”, these plants actually grow from storage organs such as tubers (swollen underground stems, as with potatoes), corms (flattened underground stems, as with crocus), or rhizomes (thickened, often horizontal, underground stems as with the perennial bearded iris). 
           
Tuberous begonias come in red, pink, orange, salmon, yellow, and white and can grow to a diameter of 12 to 14 inches. Although they can't be planted in the garden until mid-May, you can get a jump on the season by planting tubers in shallow flats or pots in March or April.
           
For indoor starting, fill containers with coarse peat moss, or soilless medium. Press the tubers into the medium three to four inches apart, with the concave side up. Place containers in a dark room at 65 to 70 degrees F. Once the shoots start to develop, add more medium to cover the tubers. Move to a sunny window. Keep the mix moist, but avoid overwatering as tubers may rot. Fertilize every two to three weeks with liquid fertilizer according to recommended rates.
           
In mid-May, plant in a well-drained and partially shaded area. Set tubers in the ground so they are barely covered. Place 18 to 24 inches apart to allow plenty of space for growth and air circulation.  Fertilize and water when soil is dry, preferably in the morning or early afternoon to allow foliage time to dry before nightfall. This reduces the chance of disease.
           
Once the frost has killed the foliage, dig the tubers, remove the foliage, and dry the tubers for two or three days.  Store in peat moss or sawdust in boxes, not plastic bags. Place in a storage area that is dry and about 50 degrees F.
Gladiolus corms can be planted as early as May 1 though, by staggering the planting dates (every two weeks until mid June), you can have flowers all summer long. Set the corms four to five inches deep and five to six inches apart. You can grow them in rows a foot or so apart, with a wider aisle every 3 rows. Use a granular organic, or bulb fertilizer, mixed into the soil at planting.  Keep plants watered if soil starts to dry between rains.
           
When foliage has dried in late fall, dig the corms, brush off the soil, and snap off the dead tops and old corm. Spread in a dry, cool place for three or four days to dry. Pack in sawdust or dry peat moss, and store in a dry, cool place at 35 to 40 degrees F. Check periodically throughout the winter for rot or rodent damage.
           
Canna, a tall plant with bright red flowers, can grow to a height of three to eight feet, depending on variety and climate. Like the begonia, it can be started indoors in pots (follow directions above), or planted directly in the garden in mid-May.
           
Choose a well-drained location with full sun. The hotter the spot the better, as cannas love heat. Planting cannas by the south side of the house or near paved surfaces where they will get plenty of heat is ideal. One limitation to growing in cool climates, and getting them to bloom, is cold summer nights. Plant the rhizomes a few inches below the surface and 18 to 24 inches apart. Water thoroughly after planting, and fertilize beginning when shoots first appear.
             
When foliage has been killed by frost in fall, remove the dead tops and dig up the rhizomes. Shake off excess soil, and let dry for a day. Store in dry peat moss or sawdust in boxes (not plastic, as these keep bulbs too wet), baskets, or burlap sacks in a dry, 45 to 50 degree F location. Do not allow to freeze.  If plants are in pots, merely cut the frosted foliage off and place pots in a non-freezing but cool location.  You don't need to water until next spring.
           
Canna can get several diseases, the most important being one of several viruses.  These have spread widely in recent years through the sale of infected plants.  If your plants have unusual streaking, distortion, or brown areas, they likely are virus-infected, and should be discarded in the trash not the compost.  When buying new plants, choose ones listed as virus-free from reputable firms.
           
Dahlias are very popular, coming in most colors, many flower styles and sizes, and on plants from one foot to 6 or more feet high.  Treat similar to cannas, only stake plants that will get over two feet high (usually with a single stake), and keep the winter storage material for tubers slightly moist (but not wet).  Dahlias grow better than cannas in cool climates.
           
If you want less common summer-flowering tender bulbs, consider the montbretia (Crocosmia) with its tall flower spikes in red, orange or yellow in mid-summer; white spider lily (Hymenocallis); Guernsey lily (Nerine), often in reds and pinks; or the white fragrant spikes of tuberose (Polianthes).  Caladiums are a foot or two high, grown for their colorful leaves, not flowers.  From their tubers arise elephant ear-shaped leaves in all many bright colors and combinations, particularly red, pink, white, or green.  These tropical plants are a good choice for shade and warm sites, as are the related and larger elephant ears (Colocasia, Alocasia). 


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