Bulb · Iridaceae
Garden Gladiolus
Gladiolus × hortulanus
Plant the corms in spring and gladiolus answers with tall spires of color from late summer to fall.
Full sun
Every 5–7 days
41–86°F · 5–30°C
60–90 days
Overview
Gladiolus is the flower that turns a plain summer border into something with real presence, sending up tall stems of funnel-shaped blooms that open from the base upward. Part of the iris family, it grows from a corm, a swollen underground stem that acts like a bulb and keeps the plant fed. Its upright, sword-shaped leaves earned the old name sword lily, and a run of glads along a fence or at the back of a bed gives a garden its summer backbone.
These warm-season flowers go in as spring-planted corms and reward a little planning. Set them out after frost and they bloom 8 to 12 weeks later, so staggering the plantings every week or two keeps the border, and the vase, in fresh cut stems all season. Gardens in zones 7 to 10 can leave the corms in the ground over winter, while those in colder places lift them each fall and hold them dry until spring.
Fitting glads into a home routine is easy, since they ask mainly for full sun and steady moisture. Grow them in a dedicated cutting row and they slot neatly into a weekly rhythm of picking stems for the table. Keep the drainage sharp and give the tallest spikes a stake, and there are always armfuls ready to bring indoors.
Care
The short version: plant the corms in full sun in rich, well-drained soil after the last frost, keep them evenly moist at about an inch of water a week, and lift the corms for winter where the ground freezes.
Light
Glads want full sun, ideally six or more hours a day, to raise strong spikes that stand tall without help. They will take a little afternoon shade, but in too much shade the stems stretch, lean, and carry fewer flowers.
Water
Keep the soil evenly moist through growth and bloom, which comes to about an inch of water a week. Steady moisture fills out the flower spikes, but the corm rots in waterlogged ground, so drainage matters just as much.
Soil
Plant in fertile, well-drained loam enriched with organic matter, and avoid heavy clay that holds water around the corm. A near-neutral pH of 6.5 to 7.0 suits them best.
Temperature
Glads grow across a wide range, roughly 41°F to 86°F (5°C to 30°C), once the season warms. They are tender to frost, so the corms go in only after the last cold snap and come out before the ground freezes hard.
Humidity
Ordinary outdoor humidity is plenty, with no number to chase. Air moving through the planting matters more, since still, damp conditions invite botrytis and corm rot.
Feeding
Glads are average feeders that do best on a soil test and a balanced fertilizer. Feed once at planting and again as the flower spikes form to support both the blooms and the corm building below.
Pruning
Cut the spent flower spikes once they finish so the plant does not spend itself on seed. Leave the foliage until it yellows and dies back on its own, since those green leaves recharge the corm for next year.
Repotting
In cold zones, lift the corms each fall and replant in spring rather than leave them to freeze. Where they overwinter in place, dig and divide the crowded clumps every few years to keep the flowers full-sized.
Size & spacing
Spikes range from 1 to 6 feet (30 to 180 cm) tall depending on the type, with the tallest needing a stake. Each plant spreads only 12 to 24 inches (30 to 60 cm), so the corms can sit fairly close in a cutting row or block.
When to plant
Gladiolus lives for the warm season and takes no frost, so its calendar shapes the whole summer display. Plant the corms in spring once the soil has warmed, set out a fresh batch every week or two for a rolling show, and the spikes open from late summer into early fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring, after the last frost once soil has warmed; plant in succession 7-14 days apart for continuous bloom.
- Harvest: Late summer into early fall, about 8 to 12 weeks after planting.
Hardiness
USDA hardiness zones: 7–10
Temperature: down to -18°C
Troubleshooting
Most gladiolus trouble begins underground or arrives on the corm, out of sight of the border. Catch the early signs on the foliage and at the base and you can act before a planting, and a season of cut stems, is lost. Match what you see below, then step in while it still helps.
Yellowing foliage and corms failing below the soil
When the display falters and the corms turn soft and brown within, the usual cause is fusarium wilt or corm rot, which settle into ground that drains poorly. A cool, wet stretch can invite botrytis or crown rot at the base as well. An infected corm is past rescue, so lift and discard the affected ones, put the drainage right, and begin again with firm, healthy corms in a fresh bed for next season's arrangement.
Fix:
- Remove and destroy affected corms and plants
- Improve soil drainage
- Rotate planting location
- Plant only firm, healthy corms
Silvery streaking and buds that never make it to the vase
That silver flecking on the foliage, and buds that dry before they open, is the mark of gladiolus thrips, small insects that graze the leaves and shelter inside the flower bracts. They usually arrive on the corms, so the marks appear before the culprit does. Cut away the worst spikes, set out sticky cards to follow the numbers, and treat or discard any corms before they go into storage, so next summer's display stays clean.
Fix:
- Remove and destroy heavily infested flower spikes
- Use yellow or blue sticky cards to monitor
- Apply an appropriate insecticide labeled for thrips if needed
- Treat or discard infested corms before storage
Toxicity
Gladiolus earns its place in the garden but not the home interior, since it is poisonous to pets and grazing animals, and the buried corm is the most dangerous part. The leaves, flowers, and corms all hold an irritant that brings on drooling, vomiting, and lethargy when eaten. Keep animals out of the beds and put corms well out of reach during planting and storage.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A cat that samples the plant tends to drool and be sick, then settle into a quiet, listless spell. The corm carries the strongest dose, so a cat with access to a dug-up corm is the real concern.
Dogs Mild
A dog that helps itself often drools, feels queasy, and passes loose stool within a few hours. A stored corm left within reach is what causes the worst of it.
Horses Mild
A horse grazing the leaves may drool, lose its appetite, and turn dull for a while. Since the corms hold the most irritant, keep them away from beds and open trenches.
Rabbits Toxic
The same irritant unsettles a rabbit's delicate gut, bringing drooling and a loss of appetite. Set the leaves, flowers, and corms well beyond a rabbit's reach.
Livestock Toxic
Cattle, goats, and sheep can scour and grow listless after grazing foliage or unearthing corms. Fence stock away from the planting and clear any lifted corms safely.
Birds Toxic
A bird that pecks the leaves or scratches up a corm risks drooling, vomiting, and lethargy. Treat every part of the plant as out of bounds for them.
People Caution
No part of the gladiolus belongs on the table, and the corm especially can irritate the mouth and stomach if swallowed. Keep curious children away from corms during planting and storage.
Keep corms and bulbs out of reach of pets, especially during planting and storage when corms are accessible.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Most garden glads are hybrids chosen by color to suit a scheme, but a few distinct species stand out for their fragrance and staying power.
Gladiolus murielae
For scent as well as sight, this is the fragrant Abyssinian or peacock gladiolus, its white blooms lit by a deep purple throat.
Gladiolus × byzantinus
This dependable Byzantine heirloom offers magenta flowers and returns of its own accord down to about USDA zone 6.
How to propagate
Gladiolus quietly multiplies itself underground, so the fall lift becomes a yearly windfall of free plants for next summer's beds.
Bulbs & cormsEasy
Spring at planting; lift and separate in fall · One growing season
The simplest way to build up a collection is to lift the corms in fall and replant them the next spring. Each parent forms a fresh corm on top, often with a ring of little cormels around the base, and the full-size corms bloom again within a single growing season.
DivisionEasy
Fall when lifting corms · One growing season
As you lift the corms, twist the small cormels from the base of the parent to start new plants. The full-size corms flower next season, while the smallest cormels need a year or two of growing before they reach blooming size.
SeedModerate
Spring · Two to three years
Raising glads from seed is a patient pursuit, mostly for breeders after new colors. Sow in spring and expect two to three years to pass before each seedling builds a corm large enough to flower.
Myths
Gladiolus flowers and leaves are safe for pets to nibble.
It looks harmless enough in the border, but every part of the plant carries an irritant, and the ASPCA lists it as toxic to cats, dogs, and horses. A single nibble brings drooling, vomiting, and a tired, off-color animal, and the buried corm is the most dangerous part of all. Keep pets clear of the foliage and, above all, the corms.