Plant gladiolus corms outdoors about two weeks before the last frost in a sunny spot with well-drained soil, then repeat every two weeks for a longer bloom, and dig them in fall in cold climates. Illinois Extension says gladiolus are planted from a corm, an energy-storage structure, and Iowa State says they perform best in a sunny location and need well-drained soil. Flowers normally open about 8 to 10 weeks after planting (Iowa State). Depth and winter storage temperature are the two numbers the sources give as ranges, and both are laid out below.
- Sun
- Sunny location (Iowa State)
- Origin
- Africa
- Soil
- Well drained; consistent watering (Illinois)
- Planting depth
- 2–6 in by corm size
- Spacing
- 6 in apart for large corms (Iowa State)
- Bloom time
- About 8–10 weeks after planting
- Storage
- 35–50°F, dry and cool
What gladiolus grow from
Gladiolus grow from corms (Illinois Extension). Some of the extension pages we used call them bulbs, but the plant itself is a corm. Illinois Extension says gladiolus are tender, meaning the cold of a northern winter can kill them if they are left outdoors.
When to plant gladiolus
Illinois Extension says corms can be planted outside two weeks before the last frost date. To lengthen the season, plant more every two weeks until early July. Iowa State says gladiolus normally bloom about 8 to 10 weeks after planting, so a planting made every two weeks gives flowers in waves rather than one burst.
How deep to plant gladiolus
| Source | Planting depth | Spacing |
|---|---|---|
| Iowa State, large corms | 4 to 6 inches | 6 inches apart |
| Iowa State, small corms | 3 inches | — |
| Illinois Extension | 2 to 6 inches, by size | — |
The range is 2 to 6 inches, and the rule underneath it is the same in both sources: larger corms go deeper. Iowa State’s figures sit inside Illinois Extension’s range.
Planting steps
- Find a sunny site. Iowa State says gladiolus perform best in a sunny location with well-drained soil.
- Plant two weeks before the last frost. Illinois Extension gives this date for planting outside.
- Set corms by size. 4 to 6 inches deep and 6 inches apart for large corms, 3 inches deep for small ones (Iowa State).
- Plant again every two weeks. Repeat into early July for a staggered bloom (Illinois Extension).
- Water consistently. Illinois Extension says gladiolus need well-drained soil but consistent watering.
Digging and storing corms
Iowa State says to carefully dig the plants with a spade in late summer or early fall. Dry the corms for 2 to 3 weeks, cut the foliage off 1 to 2 inches above the corms once it has died back, and store them cool.
Storage temperature is where the sources differ.
Iowa State
Penn State
Both together
Penn State says to store the bulbs through the winter in paper bags, boxes or mesh bags in a cool area. The overlap point is our arithmetic. If your storage space is steady at 40 to 45°F, both sources are satisfied.
Propagating from cormels
Iowa State says to save the small corms for propagation, or discard them.
Common gladiolus problems
Grow these next
Gladiolus pairs with other summer bulbs that are lifted in fall. Dahlia tubers follow the same dig-dry-store routine, and freesia is another corm that is lifted and stored where winters are cold. For a summer bloomer that stays in the ground, see the lily guide.
Frequently asked questions
When do you plant gladiolus corms?
Illinois Extension says corms can be planted outside two weeks before the last frost date, and that planting can be repeated every two weeks into early summer to stretch the bloom.
How deep do you plant gladiolus?
Iowa State says large corms go 4 to 6 inches deep and 6 inches apart, and small corms 3 inches deep. Illinois Extension says 2 to 6 inches depending on corm size.
How long after planting do gladiolus bloom?
Iowa State says gladiolus normally bloom about 8 to 10 weeks after planting.
How do you store gladiolus corms over winter?
Iowa State says to dig the plants in late summer or early fall, dry the corms, and store them at 35 to 45°F (2 to 7°C). Penn State gives 40 to 50°F (4 to 10°C) for summer bulbs stored through winter. Together that is a 35 to 50°F range.
Do gladiolus come back every year?
Not where winters are cold. Illinois Extension says gladiolus are tender and can be killed by cold winter temperatures if left outdoors, so the corms are dug and stored.
Sources
- How Deep Should I Plant Gladiolus Bulbs?, Iowa State University Extension, Yard and Garden
- How Do I Overwinter Gladiolus Bulbs?, Iowa State University Extension, Yard and Garden
- Summer and Fall Blooming Bulbs, Penn State Extension
- Tender Bulbs Make Summer Delights, University of Illinois Extension
Dahlia
Freesia
Lily