The gladiolus, known for its tall, dramatic flower spikes, is a favorite for cutting gardens and summer borders. This popular flower originates from a specialized underground storage organ called a corm, which is a modified, solid stem base that stores nutrients. This differs from a true root or bulb. The plant’s distinctive, sword-shaped foliage gives it its name, derived from the Latin word gladius meaning sword. Commonly grown as an annual in cooler climates, the gladiolus requires specific handling of its corm to ensure a spectacular bloom display each season.
The Difference Between Roots and Corms
The gladiolus corm is a biological adaptation that allows the plant to survive dormancy, functioning as a subterranean food reservoir. A corm is a swollen, compressed stem base, fundamentally different from a true root. Roots primarily anchor the plant and absorb water and minerals from the soil. The corm stores starches and carbohydrates, providing the energy needed for the plant’s initial growth and the development of its large flower spike.
Structurally, the corm is encased in fibrous, papery tunics, which are dried leaf bases that protect against damage and moisture loss. The basal plate, a flat area at the bottom of the corm, is where the true roots emerge for absorption. The top of the corm features nodes containing buds; the largest bud develops into the main shoot and flower spike.
During the growing season, a new corm forms directly on top of the old one. The old corm shrivels and dies as its stored nutrients are depleted. Small, pea-sized offsets called cormels also develop around the base of the new corm. These cormels are miniature clones that can be separated and grown over two or three seasons to reach flowering size, serving as a primary means of propagation.
Preparing the Soil and Planting Corms
Successful planting begins with selecting a location that provides ample sunlight, receiving a minimum of six to eight hours of direct sun daily. This is necessary for vigorous growth and the best flower coloration. Soil preparation is equally important, as gladiolus corms are susceptible to rot in heavy, waterlogged conditions.
The soil must be loose and well-draining, ideally a sandy loam enriched with organic matter like aged compost or manure. If the existing soil is heavy clay, incorporating organic material or planting in a raised bed ensures proper drainage. A soil pH range between 6.5 and 7.0 is recommended for optimal plant health.
Corms should be planted with the pointed side facing up, where the main shoot emerges, and the flat basal plate facing down. The recommended planting depth is typically four to six inches, with larger corms planted deeper than smaller ones. Space them six to eight inches apart to allow for air circulation and growth. To ensure a continuous display of flowers, practice successive planting by setting out new corms every two weeks from the last expected frost date until early July.
Seasonal Care and Winter Storage
Once planted, consistent moisture is required, especially as the tall flower spikes develop. Gladiolus plants need about one inch of water per week, requiring deep watering during dry weather to keep the soil evenly moist. Applying a layer of mulch helps maintain moisture and suppress weeds.
Taller gladiolus varieties often require staking to prevent heavy flower spikes from bending or breaking. It is most effective to place a sturdy stake next to the corm at planting time to avoid damaging the root system later. As the flower stalk elongates, tie it loosely to the support using soft twine or plant ties.
Lifting and Curing Corms
In regions where winter temperatures fall below freezing, corms must be lifted and stored indoors. Dig up the corms in the fall after the foliage has started to yellow, often following the first light frost. Gently lift the plant using a garden fork, and cut the foliage back to a stub of one or two inches above the corm.
The freshly dug corms must undergo a curing process to dry them out and form a protective outer layer, which prevents rot during storage. Spread them in a single layer in a warm, dry, and well-ventilated area, away from direct sunlight, for two to three weeks. After curing, remove the old, shriveled mother corm from the base of the new corm, and separate any attached cormels.
Storing Corms
Healthy, firm corms are placed into a storage container that allows for air circulation, such as a mesh bag, a paper bag, or a cardboard box layered with newspaper. The ideal storage conditions are cool, dark, and dry, with a temperature range between 35 and 50 degrees Fahrenheit. Check the stored corms monthly for signs of mold or softening, ensuring decaying corms are removed before they affect the rest of the stock.