How to overwinter gladiolus bulbs

Written by lee roberts
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How to overwinter gladiolus bulbs
Preserve your gladiolus for another season. (Jupiterimages/Polka Dot/Getty Images)

Gardeners who live outside gladioli hardiness zones can save the bulbs or corms from one growing season to the next by protecting them during the winter. The advantage is that you will save money because you will not have to purchase new gladiolus corms. Good preparation is the key to keeping your glads happy over the winter. You will also have to be willing to go out and dig the bulbs from the garden after the outdoor weather has turned cold.

Skill level:

Things you need

  • Pesticide
  • Paper bag
  • Cardboard box or pantyhose

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  1. 1

    Dig your gladiolus bulbs out of the ground soon after the first frost in the fall and before their leaves turn brown completely. Exercise caution while digging near your gladiolus to avoid nicking, cutting or impaling the corm.

  2. 2

    Loosen the soil around the corm. Grasp the stem and pull gently straight up and out of the ground. Shake and brush the corm with your hand to remove excess dirt. Inspect the hole and surrounding area and collect any cormels, small subsidiary corms. Place the cormels in a paper bag for future planting.

  3. 3

    Label and segregate your corms according to variety so that you will know when your gladioli will bloom in the summer.

  4. 4

    Cure the corms by placing them in a room with good air circulation. Maintain a room temperature of between 21.1 and 26.7 degrees Celsius (70 and 80 degrees Fahrenheit) for two to four weeks.

  5. 5

    Inspect the corms for dryness. Examine the new corms that the original corms you planted produced during the growing season. Identify the old corms by their dry and shrivelled look and feel. Snap or pull apart the loose, old corms from the new corms. Discard the old corms.

  6. 6

    Cure the new corms to heal the scar you created when you separated the new from the old. Inspect the corms and discard any damaged ones.

  7. 7

    Dust the corms with carbaryl, a pesticide that helps to reduce thrip activity.

  8. 8

    Place the corms in a room where the temperature is between 4.44 and 10 degrees Celcius (40 and 50 degrees Fahrenheit). Choose among several methods to store the corms over the winter, including putting the corms in open, paper bags; hanging them in pantyhose; laying them flat in cardboard boxes; or laying them on mesh screens.

  9. 9

    Inspect corms periodically during the winter and check for overall condition and for the presence of thrips that can survive in any stage on stored corms. Identify young thrips by their light buff colour and small size, measuring roughly 1 mm (1/32 inch). Identify adult thrips by their black bodies, white belts and 1.6 mm (1/16-inch) size. Apply insecticide or introduce lady birds to control the insects.

Tips and warnings

  • Take pictures of your gladioli while they are in bloom and use the pictures as labels for the corms.
  • Plan to ensure you have enough space at the proper temperatures to overwinter your corms.

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