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 rises as a single stiff stem lined with funnel-shaped florets that unfurl one above the next, opening from the base of the spike upward. It belongs to the iris family and grows from a corm, a rounded, swollen underground stem wrapped in papery tunics that looks like a bulb and stores the plant's food the same way. Flat, rigid leaves stand edge-on around the stem like drawn blades, which is why the plant still goes by sword lily.
These warm-season flowers grow from corms set into spring soil. Planted after frost, they open 8 to 12 weeks later, and staggering the corms a week or two apart draws out a longer run of fresh, ribbed spikes. In zones 7 to 10 the corms rest in the ground through winter, while in colder zones they are lifted each fall and stored dry until spring.
Underground sits the real workhorse, the firm, disc-shaped corm that fuels the whole show. It softens and rots in soggy ground, and it can hide thrips in its tunics if stored without a look. Given sharp drainage and a stake beneath the tallest spikes, the plant lifts armloads of long-stemmed flowers into reach for cutting.
Care
The short version: set the firm corms into full sun and 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 thick, upright spikes that hold themselves erect. They take a little afternoon shade, but in deeper shade the green stems stretch thin, lean over, and set fewer florets.
Water
Keep the soil evenly moist as the plants grow and flower, which comes to about an inch of water a week. Steady moisture swells the spike full of buds, but the corm turns soft and rots in waterlogged ground, so sharp drainage matters just as much.
Soil
Plant into fertile, well-drained loam worked full of dark organic matter, and avoid dense, heavy clay that traps water against the corm. A near-neutral pH of 6.5 to 7.0 suits them best.
Temperature
Glads grow across a wide band, 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 between the tall blades matters more, since still, damp air invites gray 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, fueling both the rising buds and the corm swelling below.
Pruning
Cut the spent flower spikes once the last floret fades so the plant does not pour itself into seed. Leave the sword leaves standing until they yellow and dry on their own, because those green blades are recharging the corm for next year.
Repotting
In cold zones, lift the corms each fall and replant them in spring rather than leave them to freeze. Where they overwinter in the ground, dig and split the crowded clumps every few years so the flowers keep their full size.
Size & spacing
Spikes stand anywhere from 1 to 6 feet (30 to 180 cm) tall depending on the type, and the tallest need a stake. Each fan of leaves spreads only 12 to 24 inches (30 to 60 cm), so the corms sit fairly close in a row or block.
When to plant
Gladiolus keeps to the warm season and buckles at the first frost. Set the corms into spring soil once it has warmed, tuck in a fresh batch a week or two apart for a longer succession of spikes, and the florets 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 down at the corm or shows first as marks on the sword-shaped leaves. Read the early streaks and yellowing and the base of the stem, and you can act before a whole planting fails. Match what you see below, then step in while it still helps.
Yellowing blades over corms gone brown inside
When the sword leaves fade to yellow and the corm cut open shows brown, mushy tissue at its core, the cause is usually fusarium wilt or corm rot, which spread through waterlogged ground. Cool, wet weather can add fuzzy botrytis or crown rot right at the base of the stem. A rotted corm cannot be saved, so lift and bin the affected ones, fix the drainage, and set only firm, pale, healthy corms into fresh soil.
Fix:
- Remove and destroy affected corms and plants
- Improve soil drainage
- Rotate planting location
- Plant only firm, healthy corms
Silver streaks scored across leaves and buds
Those pale, metallic streaks and the crimped, dried buds are the signature of gladiolus thrips, slender insects that rasp the green surface and creep inside the papery flower bracts. They hide on the corms, so the silvered scarring shows up before you find the thin brown adults themselves. Cut away the worst-marked spikes, hang sticky cards to read the numbers, and treat or throw out any corms before they go 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
For all its clean color, gladiolus is poisonous to pets and grazing animals, and the buried corm is the most dangerous part of the plant. The blade-like leaves, the funnel-shaped flowers, and the firm 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 bites into the fleshy leaf or petal drools and vomits, then curls up quiet and tired. The rounded, papery-skinned corm carries the strongest dose, so a cat that claws one loose is the greater worry.
Dogs Mild
A dog that mouths the plant drools heavily, sours in the stomach, and passes loose stool within hours. A firm stored corm, chewed open, delivers the harshest reaction.
Horses Mild
A horse cropping the strappy foliage may drool, lose its appetite, and grow dull and slow. The knobby corms hold the most irritant, so keep them clear of beds and open trenches.
Rabbits Toxic
The same irritant unsettles a rabbit's delicate gut, bringing drooling and a turned-away nose at food. The blade-like leaves, flowers, and corms all stay out of reach.
Livestock Toxic
Cattle, goats, and sheep can scour and grow listless after grazing the tall foliage or nosing up a corm. Fence stock from the planting and clear away every lifted corm.
Birds Toxic
A bird that pecks the leaf blades or scratches a corm to the surface risks drooling, vomiting, and lethargy. Every part of the plant is off limits to them.
People Caution
No part of the gladiolus is edible, and the dense corm in particular can leave the mouth and stomach raw if swallowed. Keep young children away from the 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 stand apart for their scent and the look of their flowers.
Gladiolus murielae
This fragrant Abyssinian or peacock gladiolus carries pure white blooms, each one stained with a deep purple throat at its center.
Gladiolus × byzantinus
This hardy Byzantine heirloom opens vivid magenta flowers and comes back reliably down to about USDA zone 6.
How to propagate
Gladiolus builds its own increase underground, and lifting the corms each fall lays bare a fresh crop of corms and cormels for next year.
Bulbs & cormsEasy
Spring at planting; lift and separate in fall · One growing season
Lift a clump in fall and the corm's own increase is easy to see: a plump new corm sits on top of the shriveled old one, ringed by a scatter of tiny, pea-sized cormels around the base. Replant those big corms the next spring and they bloom again within a single growing season.
DivisionEasy
Fall when lifting corms · One growing season
At lifting, the small hard cormels twist off the base of the parent between finger and thumb to start new plants. The full-size corms flower the next season, while the smallest cormels need a year or two of growing before they swell to blooming size.
SeedModerate
Spring · Two to three years
Seed is a slow road, mostly walked by breeders after new flower colors. Sown in spring, each fine seedling takes two to three years to thicken a corm large enough to send up a flowering spike.
Myths
Gladiolus flowers and leaves are safe for pets to nibble.
The soft petals and glossy leaf blades look harmless, 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 away from the foliage and above all the corms.