Gladiolus

About Gladiolus

Gladiolus (glads) grow from corms and send up tall spikes of funnel-shaped flowers that open from the bottom up in late summer. They are a classic cut flower, and planting a batch of corms every week or two gives a long run of blooms. Bees visit the flowers (NC State), and the hardier Byzantine gladiolus draws butterflies and hummingbirds.

NC State lists zones 7-10, and glads overwinter under mulch in most of South Carolina (Clemson); farther north, dig and store the corms each fall. Byzantine gladiolus is hardy to zone 6 and naturalizes in old home sites and ditch banks (NC State).

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

• Sow seeds outdoors: around the last frost

Plant corms after the last frost when the soil is at least 55 F, 3-6 inches deep (2-3 inches for small corms), pointed tip up, and plant again every 1-2 weeks for steady bloom (Clemson, Penn State). In cold areas, dig corms in fall after the leaves yellow and before a hard freeze, cure them about 3 weeks in an airy spot, then store in mesh bags at about 35-45 F (Clemson, NC State, UMN).

Soil

Rich, well-drained sandy or loamy soil with organic matter; they dislike heavy clay. Keep evenly moist (NC State, Penn State).

Rich, well-drained sandy or loamy soil with organic matter (NC State, Penn State).

Feeding

• When plants are 6-8 inches tall: low-nitrogen fertilizer such as 5-10-10. Clemson suggests 3-4 lb per 100 sq ft, spread beside the plants and watered in. Follow a soil test.
• When the flower spike appears: fertilizer such as 5-10-10. Repeat at the same rate (Clemson).

Soak the ground deeply instead of sprinkling lightly every day (Clemson), and leave at least four leaves when cutting spikes so the corm can recharge (Penn State).

Harvest

Glads bloom in late summer into fall. Cut spikes in early morning or evening when the first florets show color, and leave at least four leaves on the plant to feed the corm (Penn State). Stake or hill soil around tall stems (Clemson).

Varieties (7)

Extension sources we could open document 7 gladiolus cultivars and species.

Pests to watch for

Thrips, Aphids, Twospotted spider mite, Mealybugs, Grasshoppers, Cucumber beetles, Iris borer

Diseases and problems

Gray mold (Botrytis), Rust, Mosaic viruses, Southern blight, Root and crown rot, Corm rot

In the kitchen

Safety: The corms hold the most toxin; eating plant parts can cause drooling, vomiting and diarrhea (NC State).

Pets: Toxic to dogs, cats and horses (ASPCA): can cause drooling, vomiting, diarrhea and lethargy, and the corms are the most toxic part.