Gladiolus bloom time across the US
Interactive map
See the interactive mapDrag the date and the bloom moves north across the country. Every point has its own window, and the map says where it has no records rather than guessing. Free, with nothing to sign up for. Open the gladiolus map.
City by city
Typical window, earliest first. Cultivars of the same flower can open days or weeks apart.
Taxonomy and origin
Gladiolus is a genus of perennial cormous plants in the iris family, and the name is the Latin diminutive of gladius, a sword. The reference is to the foliage: long sword-shaped leaves stand in upright fans, and funnel-shaped flowers ride on slender stalks, opening one at a time from bottom to top. Catalogs and gardeners shorten it to glads, and older American usage runs to gladiola. The family, Iridaceae, also holds crocuses, freesias and irises. How many species the genus holds is unsettled: roughly 180 corm-bearing species at one end, more than 250 in the middle, and over 300 at the other, with Plants of the World Online accepting almost 300 species and hybrids. Carl Linnaeus described the genus in 1753, taking the name from Joseph Pitton de Tournefort.
In the wild the genus is African and Eurasian, occurring in Asia, Mediterranean Europe, South Africa and tropical Africa, with its center of diversity in the Cape Floristic Region. That South African home explains the corm. Corms are flat, thickened underground stems, and in a climate with a long dry season the corm's job was to keep the plant alive while dormant until growth resumed with the spring rains. Garden gladiolus still run on that schedule: the corm fattens through summer, the plant dies down, and the next season starts on stored food, which is why so much of growing glads comes down to what happens to the corm in fall. Two wild kinds share the catalog pages with the hybrids. Byzantine gladiolus, native to the Mediterranean region of Europe and Africa, carries spikes of magenta to purple flowers that look more orchid-like than a modern glad, and it was a favorite in the old South that still turns up in old cemeteries, abandoned home sites and ditch banks. The other is the fragrant Abyssinian gladiolus, whose flowers open successively on nodding stems and carry a real scent.
Almost every glad sold in a spring bag is a hybrid. Modern garden hybrids fall into three groups: large-flowered Grandiflora at 3 to 6 feet, miniature Nanus at about 1.5 feet, and hooded-flower Primulinus at 2 to 4 feet. Grandiflora is the florist's flower and the one most people picture when they hear the name. It sits apart from the wild species genetically as well: most gladiolus species are diploid with 30 chromosomes, while the Grandiflora hybrids carry 60, their main parent species being tetraploid too. Corms sell from 25 cents to $1.50 each and cut stems bring $1 to $2 apiece, and they are bought for line, pattern and form, since the large-flowered hybrids have essentially no fragrance.
Bloom time
Gladiolus bloom in showy spikes from late summer into fall, and the date is set by the planting date more than by the season. Time from planting to first flower is given as 60 to 90 days depending on variety, and as 70 to 90 days for the large-flowered types, so a corm set out in spring opens in the second half of summer. For the group as a whole the listed bloom period is August to September, the window a bed planted all at once will hit. A Grandiflora stem can carry 20 or more buds, so a single stalk holds color for as long as the sequence takes to work from the base to the tip. The hardy Byzantine species keeps its own calendar: planted in fall, it flowers May through July and is finished before the hybrid glads begin. Because the clock starts at planting, one planting gives one wave of bloom, and spacing the planting times a week or so apart is what keeps gladiolus in flower the entire summer.
Planting corms
Plant gladiolus corms in spring, once the danger of frost has passed and the soil has warmed to at least 55 degrees Fahrenheit. Corms put into colder ground can rot before they sprout. In Mississippi the safe window works out to mid-March through mid-April depending on location, and it moves later going north. One relative is planted on the opposite schedule, since the fragrant Abyssinian gladiolus goes in after the first frost, or is started indoors for earlier bloom. Corms are set pointed end up, into ground that has been dug over and drains, because heavy clay rots them. Planting depth is where the published advice splits, and the spread is real: 3 to 6 inches depending on the size of the corm, 3 to 5 inches, about 4 inches, and a flat 4 to 6 inches. For the hardy Byzantine type the figure drops to 3 to 4 inches, and for the fragrant Abyssinian species it is given as 2 to 6 inches by corm size. Diameter also decides flower size, so plant corms 1 1/4 inches or larger across when the big spikes are the point.
Spacing depends on whether the bed is for looking at or for cutting. Garden recommendations run 4 to 6 inches apart with rows 12 to 36 inches apart, 5 to 6 inches apart, or 6 to 8 inches apart for the hardy species set in groups of 5 to 7. A cutting patch is packed tighter: corms can sit 2 to 3 inches apart in a single or double staggered row dug out as a trench, with 20 to 36 inches between rows. Arrangement matters as much as the count. In a border or an annual bed, groups of seven or more give the best effect, and groups of at least 5 do the same job for the fragrant Abyssinian type, while straight rows belong in the cut-flower patch.
Succession planting: how far apart to space the rounds
The published intervals differ from source to source, and the hardy Mediterranean species runs on the opposite calendar entirely.
Do gladiolus come back every year?
Whether gladiolus come back depends on the zone, and the sources draw the line in two different places. Hardiness for the genus is listed as zones 7 through 10; the large-flowered Grandiflora group is put at zone 7 or 8 and warmer, while a stricter reading makes most gladiolus perennial only in zones 8 to 10. Inside that band the plant asks for very little. Hardy varieties need nothing more than a good layer of mulch to get through winter, and glads overwinter under mulch across most of South Carolina. Mulch also stretches the range: covering the corms keeps gladiolus alive in zones 6 and 7, and in colder zones for certain varieties such as the Nanus hybrids.
North of that line the corms come out of the ground every fall, the same autumn chore as lifting dahlia tubers. Dig once the foliage has faded after the first fall frost, and get it done before a hard freeze of 28 degrees Fahrenheit, which can damage the corms past saving. Lift with a spade in late summer or early fall, shake the soil off the corms, and cut the foliage back to 1 to 2 inches above them. Do not wash them: gladiolus corms keep better unwashed, and the last of the soil brushes off once they are dry. Then cure. Two to three weeks in a warm, dry, well-ventilated place is the standard, with a longer cure of about three weeks at 60 to 70 degrees Fahrenheit specified for gladiolus and calla lilies, which take longer than most tender bulbs; a day or two in bright sun first speeds the drying. When they are dry, snap the shriveled mother corm off the base and throw it away. It is used up, and the new corm that formed on top of it is next season's plant.
Store the cured corms cold and dry. The standard holding range is 35 to 45 degrees Fahrenheit at about 50 percent relative humidity, with a slightly tighter 35 to 41 degrees also given. Containers should breathe: mesh bags, old nylon stockings, paper or cloth bags, or onion sacks. Storage temperature is one place where the species part company. Byzantine corms lifted before frost are held at 45 to 50 degrees Fahrenheit, and the fragrant Abyssinian type is stored far warmer, at 60 to 70 degrees with some ventilation. Dust the corms with a fungicide bulb dust before they go into the bag to head off storage disease, and leave the husks on. After that it is a matter of checking the bags through winter and pulling anything soft. A corm dug, cured and stored properly can go back in the ground year after year.
Winter, zone by zone
What happens to the corms in fall depends on the zone and on the type, and the line falls between the tall garden hybrids and the small hardy ones.
Why gladiolus will not bloom
A fan of healthy leaves and no flower spike points at the corm before anything else. Plants raised from the small cormels that form around the base of a corm, or from seed, take several years to reach flowering size, so a patch started from saved cormels puts up foliage for several seasons before it puts up a spike. An old planting has the reverse problem. Corms multiply where they sit, the clump thickens, and the flowers thin out, which is why gladiolus clumps are dug and divided every few years to keep them vigorous. Planting date belongs in the same list, since a corm set out late runs out of warm weather before the spike is ready to open.
Light and water come next. Gladiolus flower best in full sun, and a bed shaded through the afternoon by a fence or by a shrub that has grown up since planting will make leaves and little else. Feeding is a common wrong turn, because glads need only average soil fertility and a heavily fed bed gets nothing extra for it. Water is the real lever during the weeks the spike is forming inside the leaf fan: about an inch of water a week is what good spike development takes, and a dry spell then costs flowers that cannot be made up later in the season.
Buds that form and then fail are a separate failure with a separate cause. Thrips feeding inside the closed buds can injure them badly enough that all of the blossoms on a spike are ruined, which stands behind the common report of glads that brown at the tip and never open. Sorting the corms is the part of the answer that happens in spring, before anything is planted: inspect the whole bag and discard every infected corm. Forcing is not an option. Nothing sprayed or fed will pull a spike out of a corm that has not made one, and the levers a gardener holds are corm size, sun, water and the planting date.
No spike, or a spike that disappoints
The checks below run in order, from what went into the ground to what is feeding on the plant now.
Falling over and staking
A gladiolus that falls over was usually planted too shallow, so the first fix is underground. Corms set 4 to 6 inches deep hold the tall varieties straighter and cut how much support they need. Hilling soil up on both sides of the row does the same work from above and gives good support. After that it is hardware. Large-flowered types have to be staked individually as soon as the sword-shaped flower heads appear. The rule that saves the most plants is about timing: put the stakes in at planting time, and place them where they will not go through the corm. A stake driven in beside a plant already in bud is being pushed blind into the one part of the plant that has to survive the season. Some gladiolus never need any of it. The Nanus types rarely need staking, because their stems are sturdy and proportional to their shorter height, and breeders have taken the same route with compact hybrids: 'Flevo Jive' stands 12 to 24 inches on stems that hold themselves up.
Thrips and other problems
Gladiolus thrips is the pest that costs the most flowers, and it works out of sight, inside the leaf sheaths and the closed buds. The insects are tiny, cream to dark, about the size and shape of a grass seed, and their feeding leaves silvery depressed areas often flecked with black specks. A light infestation shows as brown or silvery speckles and streaks on the leaves, while a heavy one stunts and distorts leaves and flowers until they brown and die. On the flowers the damage reads as deformity and discoloration, and the corms go soft and prone to decay. Adult females are about 1/16 inch long, so gardeners work from the streaking and rarely see the insect itself.
The insect travels on the corm. Gladiolus thrips overwinter readily on corms dug up and stored indoors, and on corms left in the soil, and since they cannot survive winter outdoors in the northern part of the continent, their yearly return to cold gardens comes from infested corms shipped around the country. Numbers climb fast once a planting is infested: development takes two to four weeks, so nine or more generations occur in a year, and one female lays 100 to 200 eggs over a life of 35 to 40 days. Control therefore runs through the corms in fall and the thermometer in winter. NC State Extension's instruction for corms going into storage is to clean them gently, soak them in bleach at 4 teaspoons per gallon of water for three hours, and dry them thoroughly before boxing them up. A competing recipe uses Lysol at 4 teaspoons per gallon for six hours, with a third version at 1 1/4 tablespoons of disinfectant per gallon for three hours. Cold does part of the job by itself, since corms held at 35 to 40 degrees Fahrenheit for at least four months lose the thrips riding on them, with 40 to 45 degrees given as the alternative figure.
Thrips are not the whole list. Gladiolus is susceptible to botrytis, crown rot, rust, wilt and mosaic virus, with aphids, mealybugs and spider mites to watch alongside them, and fusarium rot, gray mold and aster yellows belong on the list too. Virus deserves more attention than it gets from most gardeners: viruses can destroy the value of a gladiolus crop, and serious infections have run through plantings across a whole state in some years. Grasshoppers and cucumber beetles chew flowers and foliage, and corm and stem rots stay active in storage, developing when curing or storage conditions went wrong.
What actually goes wrong, ranked
Across thirty-five gladiolus threads and question pages sampled from garden forums, winter and the corm take most of the traffic. Garden.org supplied ten of them, Houzz and GardenWeb fourteen, Dave's Garden eight, and three smaller boards one each; the complaints below are ordered by how often they came up.
Six of the thirty-five threads, the largest single group. The answers split between corms that rotted and corms that came back for years, with posters blaming mulch depth and drainage for the difference.
Three threads asking why a planting that looks healthy from the leaves up produced no spike.
Three threads. A dry, stuck bud looks the same whatever caused it, so it gets blamed on watering or the weather about as often as on thrips.
Two threads. First found in Florida in 1932, the pest is now recorded in almost all states, and both threads turn on the same question of what to soak the corms in before they go into storage.
Two threads. Yellowing foliage late in the season is the signal to dig, which is what makes the same color in July worth a second look.
Two threads, one of them a pot, the other from a gardener whose corms came up scattered across a bed and wanted them consolidated.
One thread. Storage failures trace back to washing the corms, holding them too warm, or sealing them in plastic, and the cluster of small cormels around the base gets read as disease.
One thread. Gladiolus is listed as deer resistant and rabbit resistant, which is a long way from untouched.
Gladiolus types worth telling apart
Two groups do most of the work in American gardens: the tall Grandiflora hybrids grown for cutting, and the Nanus types, which run 18 to 24 inches, open a few weeks earlier, and carry a more open, butterfly-shaped flower. Badges mark the cards that come back on their own or carry scent; the near-black sorts that anchor a bed of red flowers are Grandiflora hybrids like the rest.
Cutting gladiolus for the vase
Cut the spike while most of it is still in bud. How early is the one point the sources argue over. Clemson puts it at the first floret showing color, which it gives as the stage for the best quality cut flowers. Mississippi State Extension holds stems meant for local use until the lower two or three florets are showing color or the lowest one has opened, and cuts earlier, when the lowest buds are only starting to color, for stems that have to travel or go into storage. A third instruction lands between the two: cut stalks carrying one or two open flowers. All three are earlier than the stage a gardener would call the flower's best, and that is deliberate. A spike opens from the bottom upward over a stretch of days, so a stem taken half closed spends most of its display indoors, while a stem cut at full color has already spent it in the row. What stays behind in the bed matters as much as what goes in the bucket. Leave at least four leaves standing when the corms are going to be lifted and used again. The fan is what rebuilds the corm through the rest of the season, so a spike cut low with most of the foliage attached takes next summer's flower with it. Cutting high, just above the leaves, costs a few inches of stem and keeps the plant working.
Light
Gladiolus want full sun, 6 to 8 hours of direct light a day. Heat rarely limits it, since the plant is rated heat tolerant and comes from a summer-dry part of the world. Shade limits it. The dwarf Glamini group is the one exception among garden types, pest resistant and able to bloom in full sun or in partial shade. Everything else in the genus repays the open spot twice over, because the same leaf fan that carries the spike is also building the corm that has to flower next year, and a fan working in shade hands over a smaller corm.
Water, soil, and feeding
Water whenever a week brings less than 1 inch of rain, and keep it up through the summer. The ground underneath has to drain, and the target is a pH of 6.5 to 7, which most garden beds already sit near; a bed that stays wet after rain is the one to raise or amend before any corms go into it. Feeding runs on a schedule with two dates on it: 5-10-10 at 3 to 4 pounds per 100 square feet when the plants stand 6 to 8 inches tall, and the same again when the flower spikes appear. The plant sets both dates, and the second one does the heavy lifting, since it lands while the spike is still building. Finish with a 2 to 4 inch layer of mulch, which holds soil moisture and keeps the weeds down.
USDA hardiness
Hardiness for gladiolus is published by type, and the listings do not line up. Byzantine gladiolus is given zones 6a through 10b, the fragrant Abyssinian type 7a through 10b, and the familiar garden glad appears in one data table as a tender perennial from 8a through 11b. At the warm end they agree, since all of them run to zone 10 or past it. The disagreement sits entirely at the cold end. A zone number quoted without a type attached to it is worth very little here, and the same plant ends up sold as a perennial in one catalog and as a summer bulb in the next.
Height and spread
Height is a property of the type, and across the genus the published range is 1 to 6 feet tall by 1 to 2 feet wide. Other listings put the same plants at 1.5 to 6 feet with the same spread, and at 3 to 6 feet tall by 1 to 3 feet wide, with the most common glads landing between 2 and 5 feet. Grandiflora, the florist type, accounts for the tall end at 36 to 60 inches. The species are smaller and steadier: Byzantine gladiolus stands 1 to 3 feet with a spread of 0.67 to 1.5 feet, and the fragrant Abyssinian type 2 to 3 feet by 1 to 1.5 feet. Spread carries little weight in a bed, because a corm sends up one fan and one spike and does not travel sideways in a season. What the width figure really describes is the space a single plant occupies, so glads go into the ground in blocks and rows and read as a group.
Propagation and longevity
Division is the recommended way to increase gladiolus, and the plant does most of the work itself: every season it builds a new corm on top of the old one and a ring of small cormels around the base. Those cormels are the propagation stock, and they are slow, blooming in 2 to 3 years if they are replanted each spring. Nothing speeds that up, so a gardener who wants more of a variety next summer buys corms, and one who can wait grows the cormels on in a nursery row where their bare first years do not matter. Longevity works the same way. Because the corm is replaced annually, a planting does not age out; it fails on handling, on a winter that caught it in the ground, on a storage shelf that ran warm, or on thrips that came through the bag with it.
Toxicity and pet safety
Gladiolus is toxic to dogs, cats, and horses, and the ASPCA lists the toxic principle as unknown. The signs to watch for are salivation, drooling, vomiting, lethargy, and diarrhea, and the highest concentration sits in the corms. That last detail decides where the risk actually is: not the flower border in July, but the paper bag of dug corms sitting on a garage floor through winter, which is exactly the object a dog will investigate. For people the rating runs the other way, with poison severity listed as low. Cut stems in a vase are not a household hazard, and the pet question is a storage question.
Meaning, symbolism, and the name
Gladiolus is the birth flower of August and the flower attached to a fortieth wedding anniversary, and in the language of flowers it signifies remembrance. The older associations are Roman and violent, which suits a plant named for a sword: gladiators were showered with the flowers on winning, and the link between the arena and the name comes from there. Older still, the god Pluto was said to wear a wreath of a plant traditionally identified as a gladiolus, called phasganion or xiphion in Koine Greek. The gift and birthday side of that sits on the August birth flower page.
Gladiolus myths, settled
Five claims come up often enough on garden boards to be worth settling against the sources.
The myth: Gladiolus grow from bulbs, the same as tulips and daffodils.
The reality: They grow from corms, which are flat, thickened underground stems. The difference shows in fall: the corm that was planted is used up, a new one has formed on top of it, and a cluster of small cormels has formed around the base.
The myth: Plant them shallow and they come up faster.
The reality: Planting a bit deeper is what holds the tall varieties straight without as much support. The shallow rows are the ones lying flat after the first storm.
The myth: Gladiolus come back every year anywhere, given enough mulch.
The reality: The tall garden hybrids are listed as winter hardy to zone 7. The small Nanus hybrids carry a zone 5 rating and take at least -15 F where winters are dry enough, which is where the reputation for coming back comes from.
The myth: Thrips are a summer problem out in the garden.
The reality: They overwinter readily on corms dug up and stored indoors as well as on corms left in the soil, so a bag on a storage shelf can carry an infestation straight into next season.
The myth: Cutting the spike for a bouquet kills the corm.
The reality: What protects the corm is the foliage left standing. At least two leaves, and preferably four, let the corm mature properly after the spike is gone.
What to expect, season by season
Three seasons separate a bag of corms from a patch that runs on its own stock.
The first summer belongs to the corm that came in the bag. It roots, throws its fan of sword leaves, and carries one spike, and underneath all of that the corm that paid for it is being used up while a new one forms on top with a ring of cormels around the base. Gardeners seeing that cluster for the first time usually read it as rot and throw the whole thing out.
The second summer runs on the corm you dug, cured, and stored. If it came up full sized it flowers like the one before it, and this is the season that tells you whether the storage shelf was cold and dry enough. The cormels are a separate and longer project, several seasons short of flowering size, so they belong in a spare row where the bare years cost nothing.
After that the patch becomes a question of stock. Clumps are lifted and split, since division is the standard way to keep gladiolus going, and commercial growers skip the cycle altogether, generally discarding their corms because bringing cormels up to flowering size is a long process. For a home patch the limit is nearly always the winter: corms that come through it cold, dry, and free of thrips start the next season exactly where the last one ended.
In the vase
Most of what keeps a cut spike straight and opening happens in the first hour after it leaves the row.
Flower photos
FAQ
Do gladiolus come back every year?
It depends on the type and the zone. The tall garden hybrids are listed as winter hardy to zone 7, while the small Nanus hybrids carry a zone 5 rating and are often left in the ground through zones 5 to 7 under a thick mulch. Colder than that, the corms are dug in fall and stored.
What is the best month to plant gladiolus?
There is no single month for the country, because the trigger is the ground rather than the calendar: plant once the danger of frost has passed and the soil has warmed to at least 55 degrees Fahrenheit. Mississippi gardeners reach that between mid-March and mid-April depending on where they are in the state, and colder states reach it later in spring.
How deep and how far apart do gladiolus corms go?
Space them 4 to 6 inches deep and 5 to 6 inches apart, pointed end up. Planting toward the deep end of that range helps the tall varieties stand up straighter without as much support.
Do gladiolus need staking?
The large-flowered types do, and they are staked individually as soon as the sword-shaped flower heads appear. Nanus varieties rarely need it, since their stems are sturdy and proportional to their height. Hilling soil up on both sides of a row supports a whole planting at once.
How do you keep gladiolus blooming all summer?
Plant in rounds. Corms set in succession 7 to 14 days apart keep cut stems coming, and another round every 10 days from the last frost date into early summer carries the bloom through into early fall.
Can you dig up gladiolus corms and use them again?
Yes, and in most of the country you have to. Dig once the foliage has faded after the first fall frost, cure the corms for 2 to 3 weeks somewhere warm and airy, then hold them at 35 to 45 degrees Fahrenheit.
Why are my gladiolus not blooming?
Young stock is the first thing to rule out, because cormels need 2 to 3 years of replanting before they flower. Then judge the sun the bed still gets, since glads are grown in full sun with air moving through the planting, and go over the leaves for thrips, whose feeding can stop buds opening at all.
Do gladiolus like to be crowded?
In a cutting row they tolerate it, at 2 to 3 inches apart in a single or double staggered row with 20 to 36 inches between rows. In a border they are set wider, about 6 to 8 inches apart in groups of five to seven.
Do gladiolus need water every day?
No. Water when a week brings less than 1 inch of rain and keep it steady through summer. An inch a week is the figure given for good spike development, and the weeks the spike is building inside the leaf fan are the ones to watch.
Are gladiolus poisonous to dogs and cats?
Yes, and to horses. The highest concentration is in the corms, so the bag of dug corms in the garage is the part to put out of reach.
What should not be planted near gladiolus?
Nothing is ruled out by the plant itself, but the gladiolus thrips also infests amaryllis, carnation, chrysanthemum, freesia, iris, lily, narcissus, snapdragon, and tomato. A glad row beside any of those shares the pest, which is worth knowing before you site the cutting patch.
What does the gladiolus flower symbolize?
Remembrance, in the language of flowers. It is also the birth flower of August and the flower attached to a fortieth wedding anniversary.
Interesting tips
- Frank Neuhauser won the first National Spelling Bee in 1925 on the word gladiolus, and the ragtime composer Scott Joplin wrote a piece called Gladiolus Rag.
- The species are not spread evenly across the genus range: about 260 are endemic to southern Africa, about 76 more grow in tropical Africa, and only about 10 in Eurasia.
- The flowers are edible once the anthers are removed, and they work best as a garnish or as a small container for a dip or a spread.
Related Guides & Flowers
Bearded iris
The iris family relative with the same fan of sword leaves and a completely different root to look after.
Canna lily
The other tall summer plant that gets lifted, cured, and boxed up before the first hard freeze.
Snapdragon
A cool-season cut spike for the same vase shape, and a host the gladiolus thrips is happy to move onto.
Lily
The summer bulb gardeners plant alongside glads for height, with scent the glads do not have.
Enjoying our flower guides? Add YourFlowersGuide as a preferred source on Google — it helps more readers find us.
Add to Preferred Sources