Plant gladiolus corms in spring, around your last frost: early to mid-May in Iowa (Iowa State), or as early as a month before the average last frost (Missouri, WSU). Then plant a new batch every 2 weeks until early July for flowers all summer (Iowa State, Missouri). Glads bloom about 8 to 10 weeks after planting (Iowa State). Set large corms 4 to 6 inches deep and about 6 inches apart (Iowa State), in full sun.
Gladiolus grow from corms, which look like flat bulbs. Most garden glads are tender: WSU says the large grandiflora types are hardy only in zones 7 to 10, and Mississippi State says they act as perennials in zones 8 to 10. In colder areas they are planted each spring and dug in fall. Bigger corms give bigger spikes; Iowa State suggests buying corms 1½ to 2 inches across, and Missouri lists grades from Jumbo (over 2 inches) down to No. 2 (1¼ to 1½ inches).
When to plant gladiolus by region
| Area | When to start planting corms |
|---|---|
| Iowa and the Upper Midwest | After the danger of frost, usually early to mid-May (Iowa State) |
| Missouri | Start about a month before the average last frost, then every 2 weeks; last planting no later than early July (Missouri) |
| Inland Northwest (Spokane) | As early as a month before the last frost, then every 10 to 14 days (WSU) |
| Mississippi | After the last frost, mid-March to mid-April, then every 7 to 14 days (Mississippi State) |
| Zones 8 to 10 | Glads can be perennial (Mississippi State); Clemson says most of South Carolina can overwinter them with mulch |
To have flowers before your first fall frost, count back about 10 weeks: Iowa State and Missouri both stop planting in early July. Our planting calendar shows your average last spring frost and first fall frost, which bracket the gladiolus season.
How deep and far apart to plant gladiolus
| Gladiolus corms | |
|---|---|
| Depth | Large corms 4 to 6 in, small ones about 3 in (Iowa State); Missouri adds medium 3 to 4 in and small 2 to 3 in; WSU uses 3 to 4 times the corm's diameter; Mississippi State 3 to 5 in |
| Spacing | About 6 in (Iowa State); 4 to 6 in (WSU, Mississippi State); Clemson plants 2 to 3 in apart in a trench for cut flowers |
| Planting tip | Missouri covers corms with 2 in of soil at first and fills in as the shoots grow, which also helps hold the stems up |
| Soil | Well-drained; pH 6.0 to 6.5 (Missouri) or 6.5 to 7 (Mississippi State). Missouri says soil that grows good vegetables grows good glads |
| Sun | At least 6 hours (Iowa State); full sun (NC State) |
Staking, watering and feeding
- Stake at planting so you don't stab the corms later (WSU), and tie the stems every 10 inches as they grow (Missouri). Clemson stakes or hills soil around the base instead.
- Water: about 1 inch a week (Mississippi State). WSU adds 2 to 4 inches of mulch once the shoots are up.
- Feed: side-dress when plants are 6 to 10 inches tall and again when the flower spikes appear (WSU, Clemson), using 5-10-5, 10-10-10 or 5-10-10, kept 4 to 6 inches from the stems (Missouri).
Cutting gladiolus for the vase
Cut a spike when the first floret shows color (Missouri, Clemson). Leave at least 2 to 4 leaves on the plant so the corm can rebuild for next year (Missouri, Clemson). Mississippi State notes that cut stems bend upward if laid flat, so store them standing up.
Digging and storing corms
- When: 4 to 6 weeks after bloom (Missouri), or 6 to 8 weeks after bloom when the leaves die back (WSU).
- Cure: cut the tops to about ½ inch (Missouri), dry the corms at 60 to 70°F for 2 to 3 weeks, then snap off and discard the old shriveled corm at the base (WSU).
- Store: cool and dry at 35 to 45°F (Missouri, WSU, Clemson).
- Cormels: the tiny corms around the base can be planted 1 to 2 inches deep and reach flowering size in 2 to 3 years (WSU).
- Mild winters: in zones 8 to 10 glads can stay in the ground (Mississippi State), and Clemson says most of South Carolina can overwinter them under mulch.
Thrips, rot and safety
Gladiolus thrips are the main pest. WSU says they leave silvery streaks on leaves and flowers, and Mississippi State and Clemson list them too, and NC State and Mississippi State also list botrytis and corm and stem rots. Plant only firm, healthy corms and throw out soft or moldy ones (GardenPal note). WSU says the corms are poisonous to children and pets and the plant can irritate skin, and NC State lists gladiolus as a problem for dogs, cats and horses. Store dug corms where kids and pets can't get at them, and call a doctor, poison control or a veterinarian if any are eaten.
Gladiolus in the vegetable garden
Many gardeners grow glads in rows in the vegetable garden as a cutting crop, and Missouri says soil that grows good vegetables grows good glads. One caution from WSU: don't plant gladiolus near beans or peas, which they may inhibit. See when to plant beans, when to plant dahlias and when to plant zinnias for other summer cut flowers.
Frequently asked questions
When should I plant gladiolus bulbs?
Around your last spring frost: early to mid-May in Iowa (Iowa State), or as early as a month before the average last frost (Missouri, WSU).
How deep do you plant gladiolus?
Large corms 4 to 6 inches deep and small ones about 3 inches (Iowa State), or 3 to 4 times the corm's diameter (WSU).
How long do gladiolus take to bloom?
About 8 to 10 weeks after planting (Iowa State); WSU says 65 to 100 days depending on the variety.
How late can you plant gladiolus?
Iowa State and Missouri stop in early July so the last planting blooms before fall frost.
Do I need to dig up gladiolus in the fall?
In cold areas, yes: dig 4 to 8 weeks after bloom, cure and store at 35 to 45°F (Missouri, WSU). In zones 8 to 10 they can stay in the ground (Mississippi State).
Should gladiolus be staked?
Tall types usually need it. WSU stakes at planting, and Missouri ties stems every 10 inches.
Enter your frost dates to see your last spring frost and plan gladiolus plantings.
Open itSources
- Virginia Cooperative Extension, "Companion Planting in Gardening" (SPES-620P)
- University of Maryland Extension, "Vegetable Succession and Companion Planting"
- Oregon State University Extension, "Companion Planting"
- Penn State Extension, "Herbs Make Good Plant Partners and Companions"
- University of Minnesota Extension, "Planting the vegetable garden"
- USDA Plant Hardiness Zone Map
- NOAA NCEI U.S. Climate Normals (frost/freeze data)
- Iowa State University Extension, "When should I plant gladiolus bulbs outdoors?"
- Iowa State University Extension, "How deep should I plant gladiolus bulbs?"
- University of Missouri Extension, "Gladden a late-summer garden with gladiolas"
- Mississippi State University Extension, "Gladiolus for the farmer florist"
- WSU Spokane County Extension C049, "Gladiolus" (PDF)
- Clemson Cooperative Extension HGIC 1156, "Summer- and fall-flowering bulbs"
- NC State Extension Gardener Plant Toolbox, "Gladiolus"
Pairings are summarized in our own words from extension-service guidance. Research support for many companion effects is limited, so treat them as good habits, not guarantees.