Gladiolus plants grow from specialized underground storage organs called corms, often mistaken for bulbs. These corms store nutrients to fuel growth and flowering. Each corm produces a tall flower spike with multiple blooms and sword-shaped leaves. After flowering, the original corm is replaced by new corms and smaller cormels, ensuring the plant's survival and propagation.
Gladiolus thrives in warm soil and requires a frost-free growing season. Plant corms in spring after the last frost, when soil temperatures reach at least 10°C (50°F). In colder climates, stagger planting every 2 weeks until early summer for prolonged blooms. The plant takes 70–90 days from planting to flowering, so timing ensures vibrant summer displays.
Gladiolus demands full sun (6–8 hours daily) and well-draining soil to prevent corm rot. Amend heavy clay or sandy soil with compost for nutrients and structure. The ideal soil pH is slightly acidic to neutral (6.0–7.0). Avoid low-lying areas where water pools, as excess moisture can decay corms before sprouting.
Plant corms 4–6 inches deep with the pointed end facing upward. Space them 6–8 inches apart to allow airflow and reduce disease risk. In windy areas, plant slightly deeper or stake stems later for support. For mass plantings, arrange corms in groups of 10–12 for a dramatic visual impact when they bloom.
Water newly planted corms thoroughly to settle the soil. Once growth appears, maintain 1 inch of water per week, keeping soil moist but not soggy. Apply a balanced fertilizer (10-10-10) when shoots are 6 inches tall and again as flower spikes emerge. Avoid high-nitrogen fertilizers, which promote foliage at the expense of blooms.
Gladiolus stems can grow 2–5 feet tall and may topple under wind or rain. Install stakes or grow through supportive mesh at planting time to avoid damaging roots later. Tie stems loosely with twine as they elongate, ensuring the flower spikes remain upright for optimal display.
Common threats include thrips (sap-sucking insects) and fungal diseases like botrytis. Remove affected foliage and treat with insecticidal soap or neem oil. Rotate planting sites annually to reduce soil-borne pathogens. After flowering, promptly remove spent blooms to redirect energy to corm development.
In zones below USDA 7, dig up corms after the first frost. Cut stems to 1 inch, dry corms for 2–3 weeks, and store in mesh bags in a cool (4–10°C / 40–50°F), dry place. Discard damaged or diseased corms. Replant healthy ones the following spring for another season of blooms.
