For generations, gardeners all across the United States have tucked gladiolus corms (a.k.a., glads) into their gardens in spring in anticipation of being delighted by their beautiful flower spikes that appear just a few months later. Freshly cut, long-stemmed glads are a late-summer tradition and can be found at almost any farmer's market or county fair across our land. Indeed, someone once observed that glads are "as American as apple pie."
The word "gladiolus" is derived from the Latin gladius, or sword, and makes reference to the upright, blade-like foliage of the plant. Indeed, in certain regions, the plant is referred to as "sword lily." Member of the Iridaceae plant family, glads are perennials in warmer climates that overwinter by means of underground structures called corms. There are over 250 species in the genus Gladiolus; most are native to Africa and other arid countries around the Mediterranean.
The majority of the glads planted today carry the scientific name Gladiolus x hortulanus. The latter indicates that they are hybrids of wild species of the genus. Their flowers take the form of an indeterminate compound infloresence botanically known as a "spike." Individual flowers on the spike are terms "florets." Glads are somewhat unique in that the spikes they bear are one-sided, with all florets pointing in the same direction.
Although plant breeders did not begin working with the Gladiolus genus until the late 1800s, they have had great success. Today's glads are far showier than those found growing in the wild and the color options are seemingly endless. Floral designers, flower farmers, and home gardeners are finding new and creative ways to put glads "front and center."
There are several different types of glads in cultivation today. They vary mainly in height as well as in flower form and size.
The gladiolus that grew in our grandmother's and great-grandmother's gardens were probably grandifloras. They have the classic orchid-like flower shape and come in an incredible range of colors, including pink, purple, red, yellow, green, white, and orange, plus many bi-colors. Individual flowers (florets) are 5 to 6" across. Grandifloras grow 3 to 4-feet tall and have 12 to 20 blossoms per stem. They are reliable winter hardy in zones 7 and warmer.
Dwarf grandiflora hybrids
These miniature gladioli produce 2 to 3-foot stalks and display 2-3" wide, open-faced flowers. Being smaller in size and often not needing staking, dwarf glads are a popular choice for flower gardens, containers, and cutting gardens. "Butterfly glads" are dwarf hybrids and sometimes classified as Primulinus hybrids. They feature throat blotches in contrasting colors. "Glamini glads" also fall into this category. As with the grandiflora hybrids, these corms are reliably winter hardy only in zone 7 and warmer.
Gladiolus nanus hybrids
These glads bear flowers that resemble grandifloras but are only 1/2 to 2/3 their size and usually have just 6-7 florets per spike. The color range is more limited, with most varieties having blossoms that are red, white, pink, or rose (plus bicolors). At just 18 to 24 inches tall, these smaller and less formal glads work well in pots and are a lively addition to a mixed flowerbed. Gladiolus nanus bloom in early to midsummer and will usually survive the winter in zones 5 and warmer.
Gladiolus communis var. byzantinus
Byzantine glads have naturalized in many southern gardens. Each arching 2-foot stem displays about a dozen tubular, bright magenta flowers. Bloom time is early to midsummer. The corms are hardy in zone 7 and warmer.
Dalenii Hybrids (formerly Gladiolus primulinus)
These glads have slender, 2 to 3-foot stems with flowers that are about half the size of grandiflora types. The blossoms appear to be "hooded" rather than fully open. Dalenii hybrids are hardier than grandifloras and will survive the winter in zone 6 and warmer.
As previously mentioned, the food-storage (overwintering) structure of glads are known as corms. A corm is a swollen underground stem. Each year a new corm is formed atop the old one, which shrivels and dies. On the upper surface of the new corm, buds develop from which the new plant grows the following year. The bases of old leaves are papery and cover the corm. These are called husks. The husks overlap each other and meet to form a point at the top.
While the new corm is forming atop the old one, small new corms called cormels or cormlets are produced from the base. Cormels are a chief means of propagating a certain variety of gladiolus.
Healthy corms are essential for producing vigorous plants with flowers of maximum size for each variety. A healthy corm should have smooth husks that are not discolored or damaged. The corm itself should be firm and without any dark areas or spots on the surface after the husk is removed. The base of the corm, where the old corm was removed, should be firm.
The size of the plant and flowering spike produced is directly related to the size of the corm that is planted. Corms are graded into sizes such as Jumbo (≥ 2 inches in diameter), Number One (1½ to 2 inches in diameter), and Number Two (1¼ to 1½ inches in diameter).
Glads enjoy a sunny exposure and grow well in many different soil types. If there is any possibility of selecting soils, a loam or sandy loam should be preferred. Soils having a pH between 6.0 and 6.5 and with medium fertility will give the best results. If the fertility of the soil is unknown, a soil test will help determine levels and indicate any need for improvement. Soils that produce good potatoes, corn or other garden vegetables will produce good glads. The vegetable garden is a good place to grow glads for cut flowers.
Heavy soils with poor internal drainage can be lightened by adding organic materials such as compost, peatmoss or sawdust. If sawdust is used, nitrogen in the soil will be tied up. For this reason, it will be necessary to mix about 3/4 cup of ammonium nitrate with each bushel of sawdust.
In areas where drainage is poor, glads should not be grown, or raised beds should be built to improve drainage.
To maintain the fertility in the bed, apply 2 pounds of a 5-10-5 fertilizer or one with a similar analysis to each 100 square feet of planting space. Scatter the fertilizer evenly over the soil surface before digging, and dig to a depth of 6 to 8 inches. Rotted cow manure is excellent for glads but must be mixed well into the soil so it does not touch corms or foliage, or it will encourage rots.
Glads may be planted as early as a month before the average last frost date and at two-week intervals thereafter, for a succession of blooms. The last planting should be no later than early July so that the corms have enough time to develop and mature before frost. The time from planting until bloom varies from 70 to 90 or more days, depending on weather conditions and variety.
Plant large corms 4 to 6 inches deep, medium-sized corms 3 to 4 inches deep and small corms 2 to 3 inches deep. Cover only 2 inches in the beginning and pull soil to the plants with each cultivation. Glads are often planted by digging a trench and planting corms in either a single or staggered, double rows. Corms may be spaced only 2 to 3 inches apart in the row, but if they are being grown for exhibition, they should be spaced at least 6 inches apart. Rows should be spaced from 20 to 36 inches apart.
Cultivation of glads should be only enough to keep down competing grasses and weeds. It should be shallow so that roots are not damaged. Mulches help to keep down weeds and conserve soil moisture. Straw, wood shavings and sawdust are all suitable. A 2- to 4-inch depth is required for good weed control. A light application of nitrogen should be made after a heavy mulch is applied. Preemergence herbicides can be used successfully for the control of most annual weeds and grasses to reduce cultivation.
Glads need ample water throughout the growing season. During dry weather, water the plants weekly to supply the equivalent of 1 inch of rainfall per week. Watering should soak the ground thoroughly. Avoid daily light waterings.
To ensure tall, straight flower spikes, staking is necessary, especially on the taller types. In beds or borders, individual plants will need to be staked. This can be accomplished using 1 x 1-inch stakes made from any suitable lumber. The spikes should be tied to the stakes at about 10-inch intervals with soft twine or cloth strips. In the cutting garden (as the row in the vegetable garden) 2 x 2-inch stakes can be inserted at about 10-foot intervals along the row. Wire or heavy twine is then stretched between the stakes at a spacing of 10 and 20 inches above the soil line. Individual plants can then be tied to the supporting wire or twine. Hilling up soil on both sides of the row likewise gives good support.
A side-dressing of fertilizer after the plants are well established will increase vigor. Apply a 5-10-5 fertilizer to each row. This can be applied in a band on one side of the row, keeping 4 to 6 inches away from the stems. It will be most effective if applied in a small trench several inches deep but may also be placed on the soil surface and scratched in lightly. The first application should be timed when growth is about 6 to 10 inches tall. A second application is placed on the opposite side of the row as the flower spikes start showing through the leaf sheaths. Apply about 1 pound of the fertilizer to each 100 feet of row at each application. Excessive applications of nitrogen early in the growing season results in enormous foliage growth and poor-quality flowers.
Glads do not look well in the garden unless old flowers are harvested. Since they are used primarily for cutting, spikes should be picked in their prime for maximum life indoors. Cut the spike when the first floret is showing color. To cut the spike, insert a sharp knife above the second to fourth leaf and make a slanting cut up the stem. Immerse in water immediately to promote water uptake and prevent wilting of the petals. Be sure to leave at least two, and preferably four, leaves on the plant after cutting spikes to help corms mature properly. Gladiolus spikes are very geotropic and should be stored in a vertical position until they are used.
Digging and storing corms
At our latitude, corms are not winter hardy and must be dug if they are to be used the following year. Be ready to dig in four to six weeks after blooms are finished or when the tops die off. They can be dug any time before a hard freeze. Healthy plants should be left in the soil as long as possible so there is ample time for maximum size development of the corms.
After digging, wash off soil that adheres to the corm and roots. Cut the tops to within one-half inch of the corm. Corms can be left outdoors in the sun for a day or two if the temperatures are mild, and then spread out in a light, airy place to cure. They are cured to get the surplus moisture out of the husks and corms as quickly as possible to prevent storage rots. After two to three weeks of drying, remove the old corm from the base. Sort the corms and cormels according to size. The small cormels can be saved and planted the following year, but remember it will take two to three years to produce a blooming-size corm from them.
Corms should be stored during the winter at a temperature of 35 to 45 degrees Fahrenheit in a well-ventilated area. Airy containers such as loose-weave baskets, mesh bags or old nylon stockings make good containers that may be hung out of the way. Dust corms before storage with an all-purpose garden fungicide to guard against insect and disease damage while in storage.
Credit: Portions of this article were adapted from an article by the National Garden Bureau.