Discover why these classic summer-blooming bulbs are making such a huge comeback.
From the National Garden Bureau with added notes by Larry Hodgson
Overview and History
Gladiolus are grown in gardens all over the world. Generations of gardeners have tucked these summer-blooming bulbs into their gardens in spring for the pleasure of enjoying the gorgeous flower spikes that appear just a few months later. Buckets of long-stemmed glads are a late-summer tradition. Indeed, they can be found at almost any county fair or farmer’s market.
Gladiolus are far more exotic than you may think. Yes, our grandmothers and great-grandmothers grew them. But most are native to Africa, mostly southern Africa where three quarters of the species grow. A few, though, are found as far afield as Eurasia, especially in arid countries around the Mediterranean.
Plant breeders began working with gladiolus in the late 1800s, when it became popular as a cut flower. They’ve had great success. Today’s glads are far showier than those that grow in the wild and the color options are simply incredible. You can almost find any color of the rainbow in gladiolus blooms, including green. The one exception is blue: there are no blue gladiolus.
With all that choice and such long-lasting, colorful flowers, no wonder floral designers, flower farmers, and home gardeners constantly find new and creative ways to put glads front and center.
Gladiolus owe their botanical name to the Latin word gladius, which means glaive (sword). In fact, the Romans used the word gladiolus to describe a small glaive. Glaive is an accurate description of the plant’s stiffly upright form and narrow, blade-like leaves.
Gladiolus Basic Types and Variety Names
There are some 12,000 cultivars of gladiolus (yes—I thought that would impress you!) and they have been placed into several different types for convenience sake. They vary in height as well as in flower form and size. Here are a few of them:
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 bicolors. Flowers are 5 to 6 inches (12 to 15 cm) across. Grandifloras grow 3 to 4-feet (90 à 120 cm) tall and have 12 to 20 blossoms per stem. They are reliably winter hardy in USDA hardiness zones 7–10 (AgCan zones 8–10).
Dwarf Grandiflora Hybrids
These miniature gladioli produce 2 to 3-foot (60 à 90 cm) stalks and display 2 to 3 inch (5 à 8 cm) open-faced flowers. Being smaller and often not needing staking, dwarf glads are a popular choice for flower gardens, containers, and cutting gardens. “Butterfly glads” are sometimes classified as dwarf hybrids and sometimes separately, or under the old name Primulinus hybrids. They feature throat blotches in contrasting colors. “Glamini” glads also fall into the dwarf grandiflora hybrid category. As with the grandiflora hybrids, these corms are reliably winter hardy in USDA hardiness zones 7–10 (AgCan zones 8–10).
Gladiolus Nanus Hybrids
These flowers resemble grandifloras but are 1/2 to 2/3 the size and there are usually just 6–7 flowers per stem. 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 (45 to 60 cm) tall, these smaller and less formal glads work well in pots and are a lively addition to a mixed flowerbed. Gladiolus nanus types bloom in early to midsummer. They were developed through breeding with hardy gladiolus species and usually have no problem surviving the winter in USDA hardiness zones 5–10 (AgCan zones 6–10).
These are Eurasian species adapted to temperate climates with a cold winter and a hot summer.
The Byzantine gladiolus (Gladiolus × byzantinus, syn. Gladiolus communis byzantinus) has naturalized in many gardens in both Europe and North America, including in Canada. Each arching 2-foot (60-cm) stem displays about a dozen tubular, bright magenta flowers. Bloom time is early to midsummer. The corms are hardy in USDA hardiness zones 5–10 (AgCan zones 6–10) and worth trying further north.
Even hardier is the meadow gladiolus or Turkish marsh gladiolus (G. imbricatus), similar, but a wider color range (pink to deep purple and carmine) with two large white spots with a darker border on the lower tepals. A rarer plant in gardens, its range extends into western Siberia in the wild! The corms are hardy in USDA hardiness zones 3–10 (AgCan zones 4–10).
It’s best to plant these hardy glads in the fall, as you would tulips and narcissus, and then to leave them in the ground year after year. But if you can only get them in the spring, just plant them in a permanent spot after purchase. They’ll bloom late the first year, but will adapt and start their early blooming habit the following one.
Dalenii Hybrids (formerly Gladiolus primulinus)
These glads have slender, 2 to 3-foot (60 to 90 cm) 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 USDA hardiness zones 6–10 (AgCan zones 7–10).
Abyssinian Gladiolus or Peacock Orchid (Gladiolus murielae)
You may know this tall, white, delightfully scented glad, one of the rare gladiolus with a notable perfume, as Acidanthera murielae. However, taxonomists transferred it to the genus Gladiolus as G. murielae decades ago. It’s one of the least hardy glads: USDA and AgCan hardiness zones 8–11. It may be wise to start this late bloomer indoors a month or so early to ensure it has time to flower fully in the garden
Popular Gladiolus Varieties
(All are Gladiolus Grandiflora varieties unless noted).
- ‘Costa’: Ruffled, lavender-blue flowers with darker purple edges.
- ‘Fun Time’: Ruffled flowers with a bold red rim around a bright yellow center.
- ‘Green Star’: Stunning lime-green flowers.
- ‘Lumiere’: Bold jewel-like color combination of hot pink, mauve, and violet.
- ‘Priscilla’: Creamy white flowers with pale yellow centers and pink edges.
- ‘Vulcano’: Brilliant fuchsia-pink. (G. nanus)
- Plant gladiolus corms in well-drained soil and full sun.
- You can grow them in a cutting garden, add them to your perennial garden, grow them in raised beds or containers, or plant the corms in your vegetable garden.
- Before planting, prepare the soil by loosening the planting area to a depth of 6 to 10” (15 à 25 cm). Adding compost and an all-purpose granular fertilizer will help your glads reach their full potential.
- You can expect the flowers to begin opening 80–90 days after planting. To extend the bloom time, don’t plant all the corms at once. Start some indoors in pots or trays a month or so before planting out. Start others outdoors in the spring after all danger of frost has passed. Plant additional corms every week or two until early summer (about 90 days before the first fall frost).
- Plant grandiflora types 6 to 8” (15 to 20 cm) deep. This extra deep planting helps keep the stems upright. Dwarf glads should be planted 4 to 6” (10 to 15 cm) deep. Space the corms 4 to 6” (10 to 15 cm) apart on center. You apply closer spacing if you plan to cut most of the stems for flower arrangements before they are fully open.
- Water regularly and deeply, especially during dry spells. When plants are stressed by heat and drought, they become more susceptible to pests and disease. Applying 2 to 3” (5 to 8 cm) of mulch after planting will help retain moisture and control weeds.
10 Tips for Better Gladiolus in the Garden
1. Plan for a succession of blooms.
Start planting corms in mid to late May and continue planting every 10–14 days until early July. This will keep the bouquets coming from late summer through fall.
2. Be ready to provide support for the blooms.
Glads can lean or be toppled by gusts of wind or a heavy downpour. Support the stems by tying them to bamboo canes or other stakes. To support a large planting, set solid stakes at the ends of the row and surround the stems with twine. Don’t want to bother with staking? Stick with shorter glads that grow just 2 feet (60 cm) tall.
3. Try glads in containers.
Gladiolus can be grown in planter boxes, tubs, and large urns. Grow them on their own, or pair them with cannas, colocasias (elephant ears), caladiums, or coleus. If you plant glads in nursery pots, you can just plop them into your perennial garden right before they come into bloom.
4. In cold climates, grow glads as annuals.
In areas where glads are not winter hardy, most gardeners plant fresh corms each spring. Corms are inexpensive and this option lets you try a large range of varieties over the years. Another possibility is to overwinter the corms in a frost-free space. Read more about that below under Overwintering Gladiolus Indoors.
5. Mix it up.
Glads come in so many beautiful colors and you may be surprised by which ones you like best. Explore the options by planting some assorted colors. Don’t miss the bicolors and ruffles!
6. Better soil for better flowers.
True for most garden flowers, but also your key to success with glads. Rich, well-drained soil is ideal. Poor soil can be improved by digging in plenty of compost. Avoid planting in heavy clay or in soil that gets soggy.
7. Don’t let them go thirsty.
Glads are susceptible to thrips and spider mites, which can disfigure the flowers. These pests can get the upper hand when plants are stressed by heat and drought. Keep plants as strong and healthy as possible by ensuring they get at least an inch (2.5 cm) of water per week.
8. Bigger is better.
High-quality corms may cost more, but larger corms will give you taller stems with more flowers.
9. Know when to cut.
For the longest vase life, harvest your glads when the bottom two flowers are fully open. The rest will gradually unfurl in the vase. Snap off spent flowers and recut the stem as needed.
10. Shorten the stems for easier arranging.
It can be challenging to integrate the 3-foot (90-cm) stem of glads into a tabletop arrangement. Don’t be afraid to trim the stem to size. Cut off some of the top or shorten the stem and remove a couple of the lower flowers.
In the wild, long-tongued bees and wasps, plus sunbirds, pollinate African gladioli (the ancestors of our glads). After all, a long proboscis or beak is needed to reach the nectar stored deep in the flower. In our gardens so far from their native range, where none of their normal pollinators are found, you’d think gladiolus blooms would gather little pollinator attention. However, you’ll discover they very much attract local native long-tongued insects, such as bumblebees and hawkmoths, plus, in North America, hummingbirds love them. Not honeybees, though! Their stumpy little tongues are of no use on this deep flowers.
What Is a Corm?
Besides being a word used in Scrabble, a corm is a bulblike underground storage organ developed from a swollen stem base. A true bulb, in contrast, is made up tightly packed scales. (Think of an onion: it’s a true bulb.) A gladiolus corm has a papery outer tunic and looks much like a crocus (Crocus spp.) corm . . . not surprising, since both belong to the Iris family.
Overwintering Gladiolus Indoors
In colder climates, you’ll have to bring your gladiolus indoors* for the winter if you want to save them.
*Yes, gladiolus corms often do survive the winter outdoors in cold climates, especially when they are planted in a protected spot, covered with mulch or protected by heavy snow. You can read more on that in the article Gladiolus: Hardier Than You Think.
You often read that you have to leave glads outdoors until they’ve undergone a first frost before bringing them in, as if this was a rule. But it’s more a suggestion than an obligation. It’s just that the corms grow bigger the longer they are in the ground, so it makes sense to leave them outdoors as long as possible. However, if you have other things to plant or any other good reason to bring them in before that, don’t hesitate to do so.
So, when you do dig up your gladioli, brush off the dirt roughly, then leave the corms in a dry, well-aerated spot, but protected from frost (in a garage or tool shed, for example) for 2 or 3 weeks, until the foliage starts to dry.
At this point, remove the leaves. Depending on the state of the corm, it may practically come free in your hand. If not, cut the leaves back to about ½ to 1 inch (1.25 to 2.5 cm) above the bulb.
You’ll notice see that there are, in fact, two corms. The lower one, the one the bloomed the past summer, is now all dried up. So, detach it and drop it, along with the now dead roots, into the compost. It’s the young corm on top you’ll want to keep.
Store cool and dry at about 50°F (10°C), perhaps in an aerated box in vermiculite, coir, peat moss, or shredded newspaper. Make sure you identify the corms as to their variety or, at least, color. There is nothing that looks so much alike at spring planting time as the cormes of two very different gladiolus!
If you love gladiolus, you’ll probably want to share yours. However, you can’t take cuttings of gladiolus stems (they don’t take root). As for seeds, even if you let them mature, they won’t come true to type. Almost all glads are hybrids and will give hybrid offspring with a new mix of traits! It’s through corms that you can produce new glads just like the original one!
As you dig up your gladiolus corms in late fall, you’ll notice that a new corm has formed on top of the old one. Except there is often not only one corm, but two or even three corms side by side. Separating these extra corms is the easiest and fastest method of multiplying gladiolus, as they will already be of sufficient size to flower the next year.
However, you can produce many more plants through cormels. These are tiny corms produced from the mother corm in the fall. There can be a few of them or hundreds: it depends on the cultivar and the growing conditions.
Cormels are 2 to 3 or more years from blooming, though, with the larger ones reach bloom size the fastest. So, logically, they’re the ones to keep!
You can overwinter cormels indoors under the same conditions as corms.
When you plant cormels next spring, do so in an inconspicuous spot in the garden. After all, they’ll only show grasslike foliage! Just sow them as if they were seeds. Then bring them in again next fall.
The cormels will then be much larger, looking like a miniature version of the mature corms, but are still too small to flower. It normally takes at least another year of growing in the ground before your corms will be ready to flower. So, store them again over the winter, plant them in the spring and the next fall, dig them up yet again. Just maybe they’ll be large enough to bloom the following year!
If you want to learn more about gladiolus or share your pride and pleasure in this stunning plant, there are several societies you should look into joining. Here are two:
In this, the Year of the Gladiolus, be glad you are able to grow glads!
This article was adapted from a fact sheet written by Breck’s for the National Garden Bureau and provided as an educational service. Unless otherwise mentioned, photos are courtesy of the National Garden Bureau. Purchase gladiolus corms at NGB Member Online Stores and at your local garden retailer. Please consider NGB member companies as authoritative sources for information.