By Carrie Knutson, Horticulture agent

NDSU Extension – Grand Forks County

This summer I planted gladiolus flowers in the pots in front of my house. The vertical bladed leaves added height that I was missing in my containers. The gladiolus flowers were from a mixed bag, so it was exciting to see what colors I would get. Not one of the colors, red, pink, coral, white and yellow, were disappointing.

Gladiolus flowers are grown from a type of bulb called a “corm.” The term “bulb” can mean any underground plant storage structure. These structures help the plant reproduce and/or survive during unfavorable growing conditions. Bulbs can be made from modified plant structures like stems, leaves and roots. Examples would be true bulbs, tubers, rhizomes and corms. Corms are thick shortened stems whose purpose is to store food for the plant.

Gladiolus are classified as a summer bulb. This means they are not hardy in our area and will not survive our cold winters. So, gladiolus can be used as an annual or dug up and saved to plant next year.

Corms are dug for storage after a light frost kills the foliage. Loosen the soil around the corms with a trowel or fork and then remove the corms gently from the soil. This will help prevent damage to the corms.  

Cuts in or bruises on the corm are open wounds in which disease organisms can enter. Corm injury can reduce the chances of storing the corms successfully over the winter. Select the best corms to store. The corms should be free of disease and insects.

Do not wash the corms to remove any remaining soil. Instead, wait a couple of days for the soil to dry out. Then the soil can easily be wiped off. Gladiolus corms should be cured (allowed to dry out) out of direct sunlight in a well-ventilated area at room temperature for 2 to 3 weeks. The length of curing time will depend on the curing environment conditions.

Note, the new corm will grow on top of the old corm. The old corms should be removed before winter storage. You might also find smaller corms or “cormels.” The cormels can be removed from the parent corm and saved to grow the following year. It will take a couple growing seasons before the cormels become big enough to flower.

Corms can be stored in a well-ventilated basket, mesh bags or nylon stockings at a temperature around 40° Fahrenheit. Label your bulbs so that you don’t forget what they are, especially if you have them sorted by flower color. Check your corms every few weeks to make sure no storage issues have developed.

I am still waiting for that first frost so I can dig up my corms and get them stored for winter. I can’t wait to see what my gladiolus look like next year. Happy gardening!

NDSU Agriculture Communication – Oct. 3, 2023

Source: Carrie Knutson, 701-780-8229, carrie.knutson@ndsu.edu

Editor: Kelli Anderson, 701-231-6136, kelli.c.anderson@ndsu.edu