Gladiolus, often referred to as ‘glads,’ are striking summer flowers recognized for their impressive height and vibrant, sword-like flower spikes. These dramatic plants are grown from corms, which are underground storage organs that store energy. Successfully cultivating these blooms requires understanding their environmental needs and annual care cycle. This guide provides a step-by-step approach to ensure a spectacular display of color in the garden.
Site Selection and Soil Preparation
Gladiolas perform best in full sun exposure, requiring at least six to eight hours of direct sunlight daily. Insufficient light results in less vibrant colors and weaker flower spikes. Soil quality is equally important, as corms are prone to rot if they sit in overly saturated conditions.
A well-drained, sandy loam soil is optimal for their growth, ideally with a pH between 6.0 and 6.5. If the garden contains heavy clay, significantly amend the area before planting to improve the soil structure. Incorporating organic materials like compost, peat moss, or coarse sand into the top 12 inches of soil enhances drainage and introduces nutrients.
Planting the Corms for Successive Blooms
Planting should begin in the spring after the danger of the last hard frost has passed and the soil temperature has warmed to at least 55 degrees Fahrenheit. Position the corms with the pointed growing tip facing upward. Large corms should be planted four to six inches deep for stability, especially for taller varieties, while smaller corms can be set slightly shallower. Planting too close to the surface leads to instability once the tall flower spikes emerge.
Corms should be spaced about six inches apart to allow sufficient air circulation and room for growth. Spacing them slightly closer, around five inches, can offer mutual support to the developing stems, potentially reducing the need for staking. Digging a single trench is an effective method for planting multiple corms in a row.
To guarantee a continuous display of color throughout the summer, staggering the planting is highly recommended. This involves planting a new batch of corms every ten to fourteen days, starting from the first planting date until mid-June or early July. Since each corm only blooms for about two weeks, this staggered approach ensures new flower spikes are constantly emerging, extending the period of enjoyment.
Essential Maintenance During the Growing Season
Consistent moisture is necessary throughout the active growth phase, especially during dry periods. Gladiolas require the equivalent of one inch of water per week, delivered through deep watering rather than frequent, shallow sprinklings. This ensures the root system develops deeply without encouraging surface moisture that promotes disease.
The soil should be amended with compost before planting. A balanced, low-nitrogen fertilizer can be applied once the shoots reach about ten inches in height. A second application is beneficial when the flower spike begins to show color, providing energy for bloom production.
Due to their height (up to five feet) and heavy flower load, many gladiolas require staking to prevent the stems from bending or breaking. Placing a stake near the corm at the time of planting prevents accidental damage later on.
Monitoring for pests, particularly gladiolus thrips, is important throughout the season. These tiny insects scrape plant cells, causing leaves to develop silvery streaks and preventing flower buds from opening correctly. If thrips damage is observed, treatment options include applying insecticidal soap or a systemic insecticide. Early detection is important, as thrips multiply quickly and may overwinter on the corms if left untreated.
Preparing and Storing Corms for Winter
In USDA hardiness zones 7 and colder, gladiolas are not reliably winter-hardy and must be lifted and stored indoors. The correct time to dig the corms is in the fall, approximately six weeks after the plant has finished blooming, or after the foliage naturally begins to yellow. This timing allows the plant to transfer maximum energy back into the corm.
Complete this process before a hard freeze occurs, which can damage the corms. After gently lifting the corms with a garden fork, cut the foliage back to a short stub above the corm. The next step is curing, where the corms dry in a warm, airy location out of direct sunlight for two to three weeks. Curing allows the outer husk to seal, reducing the risk of rot during storage.
Once fully cured, the old mother corm from the previous season can be easily removed from the base of the new corm. Brush off any remaining soil and inspect the corms for signs of disease or pests before storage. Store the corms in a cool, dry, and dark environment, ideally between 35 and 50 degrees Fahrenheit. Storing them in a mesh bag, paper bag, or cardboard box allows for proper air circulation, preventing moisture buildup and subsequent decay.