Daniel Gill, Merrill, Thomas A. | 4/19/2005 10:28:52 PM
By Dan Gill
LSU AgCenter Horticulturist
The tall flower spikes of gladiolus add elegance to the flower garden. Derived from species native to South Africa, the modern hybrid gladiolus (Gladiolus x hortulanus) grows from a corm and has been a favorite of Southern gardeners for generations.
We often call them "glads," but an old name for gladiolus is sword lily, which refers to its sword-shaped leaves (like the term gladiator, gladiolus is derived from the Latin word for sword).
At any rate, they are easy to grow and produce beautiful flowers in nearly every color of the rainbow. And the corms are relatively inexpensive to buy.
Select and plant gladiolus corms now through March. (You can begin to plant gladiolus corms into the garden as early as late January.). The foliage of glads will withstand late frosts. Since glads grow and bloom best at moderate temperatures, those planted during this period will bloom in April and May.
I have found from experience that planting corms after March often leads to disappointment.
Although corms planted later will grow and bloom, the intense heat of mid-summer around here weakens the plants. In addition, high populations of thrips insects that have built up by then are devastating to the flowers, and spider mites attack the foliage.
By planting glads early, they escape summer heat and pest problems during their flowering period.
As with most plants that are grown from bulbs (the term "bulb" generally is used by gardeners to refer to any fleshy underground structure including corms, tubers, bulbs, rhizomes and tuberous roots), purchasing larger, high-quality corms will produce the best results.
Look for jumbo size gladiolus corms for the best flowers. Large No. 1 and No. 2 size corms also will put on a good show.
Just keep in mind that the older cultivars and species of glads often have naturally smaller corms than modern hybrids.
I think gladioluses look best when they are planted in clumps or groups of five, 10 or more among other flowers or shrubs. With their strongly vertical growth habit, they act like exclamation points in the garden and create contrast and interest in the middle or back of mixed borders and flowerbeds.
If you want to plant them in a row, plant the corms in a zigzag double row for a fuller effect. A single row generally produces a weak, wimpy appearance, particularly if the flower spikes start to lean in various directions.
With so many colors to choose from, don’t make the mistake of planting one of each in your garden. A better effect can be achieved by choosing two or three harmonious or attractively contrasting colors and planting them together in small clumps of single colors.
Well-drained soil and a sunny location are essential for growing glads. Prepare the area for planting by digging in a 2-inch to 3-inch layer of organic matter and a light sprinkling of a general-purpose fertilizer. Thoroughly incorporate those materials into the area, and you’re ready to plant.
Plant jumbo corms about 5 inches deep, medium-sized corms 4 inches deep and small corms 3 inches deep. Leave about 4 inches to 5 inches between corms. Cover the corms with soil, mulch to prevent weeds and water generously.
The deeper planting of the jumbo corms will help reduce the need for staking them later on. But to provide extra support for the tall varieties, mound soil around the plant bases as they grow.
When the flower stalks gain height, staking still may be necessary to prevent the plants from leaning over. For a more natural look, use green-colored bamboo stakes placed out of view behind the stems and tie them to the plants in two places using green twine.
Each gladiolus corm produces one large flower spike that blooms for about a week. To extend the flowering period, plant a batch of corms every two weeks from now until mid-March. This will ensure a succession of blooms during late spring and early summer.
Glads make outstanding cut flowers, so you may want to plant some extra corms in your cutting garden, if you have one – or in your vegetable garden or some out of the way bed – for cutting. When cutting the flowers, at least four or five leaves should be left on the plant to produce a new corm capable of blooming the next year.
Hybrid gladioli are hardy here and may be left in the ground over winter. But you may find they deteriorate and cease to bloom without annual lifting of the bulbs and replanting in fresh, prepared soil.
To avoid that problem, in the late summer when the foliage turns brown, dig the corms, break off the brown leaves and the previous season’s withered corm and store the corms in a dry, frost-free location to plant next year.
If you’re an energy-conserving (read that lazy) gardener, like me, you may choose to leave the corms in the ground and see how well they return.
Some gladiolus, particularly the older cultivars, will return for years without digging and storing. The Byzantine gladiolus (Gladiolus byzantinus), also called corn lily, and the parrot gladiolus or Natal lily (Gladiolus natalensis, formerly known as G. psittacinus) are excellent, long-lived species for Louisiana gardeners. Although not easy to find, the corms generally are available from mail order companies that specialize in bulbs – if you can’t find them locally.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.