The gladiolus is a striking addition to any summer garden, known for its tall flower spikes and blade-like foliage. Proper trimming practices are necessary to maintain its appearance and ensure the health and vigor of the corm. Pruning involves steps throughout the growing season that redirect the plant’s energy away from seed production and toward recharging the corm for next year’s blooms. This process includes managing spent flowers, waiting for foliage maturation, and preparing the corms for dormancy.
Managing Spent Flowers
The first step in pruning is deadheading, which begins while the gladiolus is still actively blooming. Deadheading involves removing individual flowers as they fade to prevent the plant from diverting energy into seed development. Since the gladiolus blooms from the bottom of the spike upward, use clean, sharp shears or pinch off each withered floret without disturbing the unopened buds above it.
Once the majority of blooms on the central spike have finished, the entire stalk should be removed. Make a clean, angled cut on the flower spike just above the topmost remaining leaves. This technique leaves the maximum amount of green foliage intact, which is necessary for corm development. Disinfecting your cutting tool, such as with an alcohol solution, helps prevent the transmission of plant diseases.
Cutting Back Foliage
The period immediately following the end of flowering is the most important for the health of the gladiolus corm. Although the colorful display is over, the remaining green, sword-like leaves must be left undisturbed for several weeks. The primary function of this foliage is to perform photosynthesis, manufacturing the carbohydrates that are then transported down to the corm.
This energy transfer process strengthens the corm for the following season and typically requires the leaves to remain green for about six to eight weeks after the last bloom has faded. Cutting the foliage back prematurely starves the corm, resulting in smaller, weaker blooms the next year. Only once the leaves naturally turn yellow and begin to wilt, indicating that photosynthesis has ceased and nutrient transfer is complete, should you make the final cut.
Preparing Corms for Winter
The final pruning of the season coincides with the plant’s natural dieback, usually occurring in the late fall or after the first light frost. At this point, the fully yellowed or brown foliage should be cut down to a short stub, typically leaving one to two inches remaining above the soil line. This short stub acts as a handle for lifting the corm and prevents soil-borne diseases from traveling down the stem.
For gardeners in colder climates where gladiolus is not reliably winter hardy (generally USDA zones 7 and below), the corms must be lifted for storage shortly after this final cut. Gently loosen the soil around the plant with a garden fork and lift the entire clump, taking care not to damage the corms.
After shaking off loose soil, the corms need to be cured—dried in a warm, dry, and well-ventilated location for two to three weeks until the outer husk is firm and papery. Once cured, the corms are ready to be stored in a cool, dark, and frost-free place, such as a mesh bag or cardboard box, until the following spring.