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Late April into early May is an ideal time to plant into flower beds or borders those plants we refer to as summer-flowering "bulbs." In fact, many plants in this group do not produce bulbs at all. However, all have some type of underground storage structure which, unfortunately, cannot survive the cold temperatures of winter in the Midwest and must be dug and stored indoors each fall. For simplicity's sake, we will refer to them as bulb plants in this article, regardless of the botanical classification of their storage structure. Among the plants in this group are caladium, canna, dahlia, elephant ear, freesia, gladiolus, Ismene (Peruvian daffodil), tuberose, and tuberous begonia.
Some gardeners do not like the extra effort required to dig and store the bulbs of these plants in the fall. However, the summer display of color and unique flowers produced by most are enough to make the effort worthwhile. Additionally, saving propagules from year-to-year reduces the amount of money spent on plant material annually.
Of the afore-mentioned group of plants, gladiolus and dahlias are the most popular, but many of the others deserve at least a little space in the garden. Some are useful for specialized locations to add variety where the selection of plants adapted to those locations is limited. One such location is a shady spot. Annuals such as impatiens and begonias are often used. However, bulb plants such as caladium and tuberous begonia also are quite suitable. However, care must be taken not to locate tuberous begonias where they get any direct sun other than early in the morning or late in the evening.
Tuberous begonias should be started indoors or under protection before planting into the garden. Caladium is grown for its colorful leaves and may be started indoors or planted direction into the garden, once the soil has warmed. They both require shallow planting and adequate amounts of water during the heat of summer to keep them growing actively. Another bulb plant that thrives in wet locations with light shade is the elephant ear (Colocasia esculenta). Its large, spectacular leaves provide a tropical look and plenty of the "wow" factor. This especially is true for Thailand Giant (Colocasia gigantea) whose leaves might approach 4-6 ft. in length and 3-5 ft. in width.
Many of these summer bulb plants perform best with plenty of direct sunlight, although afternoon shade tends to help extend the life of the flower during very hot weather. Tuberose, Ismene, gladiolus, dahlia, canna and freesia all fit this category. They need warm, well-drained soil to develop rapidly and flower abundantly. Canna along with elephant ear are the best plants for providing a lush, tropical look because of their large leaves. Canna plants may reach a mature height of between 20 inches and seven feet, depending upon cultivar. As a rule, the shorter, dwarf canna cultivars are more free-flowering than the taller ones. Although cannas are tolerant of dry conditions, their optimum garden performance will be achieved with adequate amounts of water during the heat of summer. Fertilization with a garden fertilizer such as 5-10-5 applied every two weeks will keep them growing actively.
Somewhat smaller bulb plants for sunny spots include Ismene, freesia and tuberose. These species produce blooms only once per season. Most make excellent cut flowers or can be left in the garden for enjoyment. After flowering is completed, the plants must be allowed to remain in the garden for the remainder of the summer for the development of the underground storage structures. This suggests that they are best planted in a cutting garden which is away from the more ornamental section of the landscape, or they need to be mixed with other flowering annuals or perennials which will provide color when these plants are without blooms.
As previously mentioned, gladiolus and dahlia are the two most popular summer-flowering bulbs. Gladioli are available in a wide array of sizes and colors. Dwarf types only reach a mature height of 24 inches, while taller types might grow to five feet or more in height with spectacular flower spikes nearly 36 inches long. Most of our modern gladioli are inter-specific hybrids and prefer full to afternoon sun exposures. A well-drained garden loam along with protection from strong winds also is recommended. Delay planting until the soil has warmed and make several consecutive plantings to extend the flowering season. Gladiolus requires moisture during the growing season; therefore, do not allow soil to dry. After blooming has ended, watering may be reduced.
Dahlias are one of the most spectacular plants and flowers in the summer bulb group. Once flowering begins, they will flower for the remainder of the summer and into fall. In the warm days and cool nights of late summer and fall, dahlias produce spectacular shows of color as they seemingly glow in the landscape. They need plenty of moisture and adequate fertilizer for optimum performance, but are tolerant of a wide range of conditions. There are many varieties and flower types of dahlia, which may range in size from about 12 inches to those that grow nearly six feet in height. Flower size also ranges from only about an inch in diameter to those that are as large as a dinner plant. Although the taller varieties need staking or some other type of support, they can make a very colorful background for shorter flowers growing in front of them.
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REVISED: April 14, 2021