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 classic cut-flower spike, throwing up a tall stem packed with funnel-shaped blooms that open from the bottom up. The plant belongs to the iris family and grows from a corm, a swollen underground stem that looks like a bulb and does the same job of storing food. Its sword-shaped leaves give it the old name sword lily, and a row of glads down a fence is a summer fixture in many gardens.
These are warm-season flowers grown from spring-planted corms. Set them out after the frost has passed and they bloom 8 to 12 weeks later, which lets you stagger plantings every week or two for color that keeps coming. In zones 7 to 10 the corms can stay in the ground over winter, while gardeners in colder spots lift them each fall and store them dry until spring.
Glads are easy to please and ask for little beyond full sun and steady moisture. The main thing to watch is the corm itself, which rots in soggy ground and draws thrips if stored carelessly. Give the plants good drainage and a little support for the tallest spikes and they reward you with armloads of flowers for the vase.
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 push up strong spikes that stand on their own. 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 while the plants are growing and blooming, which works out to about an inch of water a week. Steady moisture builds full flower spikes, but the corm rots in waterlogged ground, so good drainage matters just as much.
Soil
Plant in fertile, well-drained loam with plenty of organic matter worked in, and steer clear of heavy clay that holds water around the corm. A pH of 6.5 to 7.0, close to neutral, suits them best.
Temperature
Glads grow happily across a wide range, roughly 41°F to 86°F (5°C to 30°C), once the season has warmed. 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 fine and there's no number to chase. Air moving through the planting matters more, since still, damp conditions invite botrytis and corm rot.
Feeding
These 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 fuel both the blooms and the corm building up below.
Pruning
Cut the spent flower spikes once they finish so the plant doesn't waste energy on seed. Leave the foliage standing until it yellows and dies back on its own, because those green leaves are recharging the corm for next year.
Repotting
In cold zones, lift the corms each fall and replant them in spring rather than leaving them to freeze. Where they overwinter in the ground, 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 row or block.
When to plant
Gladiolus runs on the warm season and has no tolerance for frost. Plant the corms in spring once the soil has warmed, set out a fresh batch every week or two for a long 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 starts underground or arrives on the corm itself. Catch the early signs on the leaves and at the base and you can step in before a whole planting is lost. Match what you see below, then act while it still helps.
Yellowing leaves with corms that rot from the inside
When plants wilt and the corms turn soft and brown, you are likely looking at fusarium wilt or corm rot, which take hold in soggy ground. Cool, wet spells can also bring on botrytis or crown rot at the base. There is no saving an infected corm, so lift and bin the affected ones, fix the drainage, and replant only firm, healthy stock somewhere fresh.
Fix:
- Remove and destroy affected corms and plants
- Improve soil drainage
- Rotate planting location
- Plant only firm, healthy corms
Silvery streaks on the leaves and buds that never open
This is the work of gladiolus thrips, tiny insects that rasp the surface of leaves and hide inside the flower bracts. They ride in on infested corms, so the damage often shows up before you ever spot the pest. Pull and destroy the worst spikes, hang sticky cards to track the numbers, and treat or toss any corms that carry them into storage.
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 is poisonous to pets and grazing animals, and the buried corm is the most dangerous part of the plant. 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 chews any part of the plant tends to drool and vomit, then go quiet and tired for a while. The corm packs the strongest dose, so a cat that digs one up is the bigger worry.
Dogs Mild
Dogs usually react with heavy drooling, an upset stomach, and loose stool, often within a few hours. A dog that unearths and eats a stored corm can get the worst of it.
Horses Mild
Horses grazing the foliage may drool, lose their appetite, and turn dull and sluggish. The corms hold the most of the irritant, so keep them away from beds and planting trenches.
Rabbits Toxic
The same irritant compounds upset a rabbit's sensitive gut, bringing drooling and a refusal to eat. Keep the leaves, flowers, and corms well out of reach.
Livestock Toxic
Cattle, goats, and sheep can scour and grow listless after grazing on the foliage or turning up the corms. Fence stock away from plantings and discard any lifted corms safely.
Birds Toxic
Backyard birds that peck at the leaves or scratch up a corm risk drooling, vomiting, and lethargy. Treat every part of the plant as off limits to them.
People Caution
No part of the gladiolus is meant for eating, and the corm in particular 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 sold by color rather than name, but a few distinct species are worth knowing for their fragrance and hardiness.
Gladiolus murielae
This is the fragrant Abyssinian or peacock gladiolus, known for its white blooms marked with a deep purple throat.
Gladiolus × byzantinus
A tough heirloom Byzantine type with magenta flowers that comes back reliably down to about USDA zone 6.
How to propagate
Gladiolus all but multiplies itself underground, and lifting the corms each fall hands you free plants for next year.
Bulbs & cormsEasy
Spring at planting; lift and separate in fall · One growing season
The everyday way to multiply glads is to dig the corms in fall and replant the following spring. Each parent corm grows a fresh one on top and often a cluster of small cormels around its base, and the big corms bloom again in a single growing season.
DivisionEasy
Fall when lifting corms · One growing season
When you lift the corms, twist the little cormels off the base of the parent to start new plants. The full-size corms flower the next season, but the smallest cormels need a year or two of growing before they reach blooming size.
SeedModerate
Spring · Two to three years
Growing glads from seed is slow work and best left to breeders chasing new colors. Sow in spring and expect to wait two to three years before the seedlings build a corm large enough to flower.
Myths
Gladiolus flowers and leaves are safe for pets to nibble.
Every part of the plant carries an irritant, and the ASPCA lists it as toxic to cats, dogs, and horses. A 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 especially the corms.