The gladiolus, often called the sword lily, is a popular summer-blooming flower that introduces dramatic vertical accents and vibrant color to any garden. These plants grow from a corm, a solid, swollen stem base that stores food, rather than a true bulb. Cultivating these flowers is a straightforward process that rewards the gardener with spectacular, long-lasting blooms ideal for cutting. This guide covers growing gladiolus from the corm stage to end-of-season care.
Selecting Corms and Preparing the Site
Successful gladiolus cultivation begins with selecting healthy, high-quality corms, as their size directly relates to the flower spike’s quality and height. Choose corms that are firm, plump, and free from mold, soft spots, or blemishes. For the largest blooms, select corms at least 1.25 inches (3.2 cm) in diameter, as these produce the strongest plants.
To enjoy continuous color throughout the summer, employ a successive planting strategy. Begin planting two weeks before the average last spring frost date and continue planting small batches every two weeks until early July. This staggered approach ensures new flower spikes emerge regularly, extending the bloom season. The planting site requires full sun exposure (at least six to eight hours daily) for sturdy growth and vivid color.
Gladiolus plants demand well-draining soil; waterlogged conditions cause corms to rot. If soil contains heavy clay, improve drainage by incorporating organic matter like compost or manure, or by planting in raised beds. The ideal soil is a sandy loam with a slightly acidic to neutral pH (6.0 to 7.0). Loosening the soil to a depth of 12 to 15 inches (30–38 cm) before planting allows for optimal root development.
Planting Techniques and Initial Support
Once the soil is prepared, plant the corm with the pointed end facing upward to ensure stable, upright growth. Large corms should be planted 4 to 6 inches (10–15 cm) deep, while smaller ones can be set at 3 to 4 inches (7–10 cm).
Space corms 5 to 6 inches (12–15 cm) apart for adequate growth and mutual support. For cut flowers planted in rows, space the rows 20 to 36 inches (50–90 cm) apart. Placing a thin layer of sand or peat moss at the bottom of the planting hole improves drainage and protects the corm from excessive moisture.
Since gladiolus plants can reach heights of two to five feet, immediate support is necessary to prevent spikes from leaning or snapping. Insert a stake (bamboo cane or thin wooden post) into the ground at the time of planting to avoid damaging the corm later. After covering the corms with soil and pressing firmly, water the area thoroughly to settle the soil.
Seasonal Care and Flowering
Consistent care promotes robust flower spikes and vibrant blooms after the foliage emerges. Gladiolus plants need ample and consistent moisture, especially during dry periods and as the flower stalks develop. Aim to provide the equivalent of one inch of water per week, ensuring the soil is soaked deeply rather than receiving light sprinkles.
Fertilization should be timed to support key growth stages. Apply a nitrogen-heavy fertilizer when the plant has two to three leaves. Follow this with a balanced, low-nitrogen formula (like 5-10-10 or 8-8-8) when the plant has five to six leaves. A final application of a fertilizer higher in phosphorus and potassium (such as 0-0-30) should be given just before the flower stalks emerge.
Monitor for pests like gladiolus thrips, which feed on buds and can cause malformed or discolored flowers. Continue staking as the flower spike grows, loosely tying the plant to the pre-inserted support stake with a soft material. For cut flowers, harvest the spike in the early morning or evening when the lowest one or two florets begin to show color.
When cutting the flower spike, use a sharp knife and make a diagonal cut, leaving at least four leaves on the plant. Leaving the foliage allows the corm to photosynthesize and store energy for next season’s growth. Place the cut spikes immediately into a bucket of water and allow them to rest in a cool, dark place before arranging them indoors.
End-of-Season Care and Storage
In colder climates (USDA zones 7 and below), gladiolus corms are not winter-hardy and must be lifted before the first hard frost. The signal to begin is when the foliage starts to turn yellow, usually four to six weeks after flowering has finished. Leaving the foliage on until it yellows ensures the corm absorbs maximum nutrients for next year.
Use a garden fork to gently loosen the soil and lift the entire plant, being careful not to injure the corm. Shake off loose soil, then cut the foliage back to within one to two inches (2.5–5 cm) above the corm. Cure the corms by placing them in a warm, dry, and well-ventilated area, such as a garage or shed, for two to three weeks.
After curing, remove and discard the old, shriveled corm at the base. Small cormels (tiny offsets) can be detached from the new corm and saved for propagation, though they take two to three years to reach blooming size. Store the new corms in a well-ventilated container (paper bag, mesh sack, or nylon stocking) at a temperature between 35°F and 45°F (2°C and 7°C) for the winter.