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how to grow gladiolus

How To Grow Gladiolus

Glads make every garden bed and every table vase look full! For a striking flower show and stunning cut flowers, grow gladiolus. This spring-planted corm (bulb), quickly produces flower spikes in a variety of colors that pop. This makes them a first choice for tucking into young perennial flower gardens that could use some added color while they reach maturity. Glads also make excellent cut flowers, both grouped in a vase or mixed with other flowers in arrangements.

How To Plant Gladiolus

Light: Gladiolus grow and flower best in full sun. Gladiolus corms will flower in part shade, but the colors will not be as vivid as when planted in full sun, and the plant won't grow quite as well.

Soil: Gladiolus like well-drained, sandy loam soil. The corms will rot if the soil is too heavy and wet. If you have clay soil, grow in raised beds and loosen the soil to 12 inches deep before planting.

Spacing: Space gladiolus corms 6 to 10 inches apart in the garden and plant corms 2 to 6 inches deep depending upon the size of the corm (plant bigger corms deeper).

Planting: Plant gladiolus corms in spring 2 weeks before your last expected frost date. To enjoy flowers all summer, plant your Glads every 2 weeks until early July. This will stagger the plantings and flowering times. You can also extend the flower season by growing early, mid and late-season Gladiolus varieties.

gladiolus corms close up

How To Care For Gladiolus Throughout the Season

Growth Habit: Gladiolus have narrow, sword-like leaves and tall flower stalks. The flower stalks can grow 2 to 4 feet tall while only spreading 1 foot wide.

Staking: Gladiolus flower stalks need to be staked, caged or supported so they don't flop over, or become deformed and curved due to summer storms. Soon after planting, push flower stakes into the ground or add supports around the corm. Do this early so as not to damage the flower. As soon as the flower stalk forms, tie it loosely to a stake with a soft material, or use flower rings to support it. Remove the stakes after the flower is harvested or fades.

Planting gladiolus in groups in the garden or next to tall bushy plants is another way to keep them growing upright without producing crooked flower stalks.

Watering: Keep gladiolus plants well watered with at least 1 inch of water a week. This amount may have to increase during periods of drought or if you're growing in raised beds.

Fertilizing: Add compost to the soil before planting gladiolus. Add an organic, water-soluble fertilizer when the plants are 10 inches tall, and again when the flowers start to show color.

Trimming & Pruning: Gladiolus are either grown as a cut flower for indoor arrangements, or as an annual flower in the garden. They don't require trimming or pruning.

The flower stalk is harvested in the morning for flower arrangements when the lower 3 blossoms on the stalks begin to open. Leave at least 4 leaves on the plant to rejuvenate the corms if you plan on saving them for next year.

In the garden, deadhead the flower stalk after the flowers fade. This will also prevent the flowers from setting seed and self sowing throughout your beds. Although these seedlings will eventually get large enough to flower, it will take years and the seedlings can become weedy.

Mulching: To preserve soil moisture, mulch plants once they emerge from the soil with a 2 to 3 inchthick layer of straw or bark mulch. Gladiolus don't compete well with weeds. If the area where you'd like to plant is weedy, weed before applying the mulch. The mulch should help with weed control as well.

Gladiolus: End of Season Care

Dividing & Transplanting needs: In USDA hardiness zones 6 and colder, gladiolus corms are best dug and stored indoors in the fall. They aren't hardy enough to reliably survive the winter cold. Here's how:

  • After the leaves have started to yellow, cut back the foliage to the ground and dig the corms.
  • Let the corms dry in a warm, airy location out of direct sunlight for 3 weeks.
  • Once dry, knock off the soil from the corms and remove and discard the old bottom corm. You may notice small cormlets attached to the new corm. You can remove and discard small ones, but keep the largest ones (about ½ inch diameter) to grow as separate plants next year. It may take 2 to 3 years of growing and saving the corms offshoots, but they will eventually become a flowering gladiolus plant.
  • Store the corms in mesh bags in a well-ventilated, dark room with temperatures between 35F and 50F.

Warm Climate Overwintering: In USDA hardiness zones 7 and 8, gladiolus corms can be left in the ground and will come back each year. Cut back and compost the tops in late fall. In colder areas of this range, mulch the corms in late November with a 4 to 6 inch thick layer of chopped leaves or straw to provide more winter insulation.

Pests/ Disease: The best way to avoid insects and disease problems on gladiolus is to buy healthy corms that are not soft or crumbly. Discard any damaged or rotting corms that you are storing. If you notice stunted, gnarly growth on one gladiolus plant during the growing season, remove and destroy the plant and corm, as it probably has a virus.

The biggest pest of gladiolus is a small insect called thrips. Thrips feed on the flowers and leaves causing characteristic streaking and discoloring on the flowers. Thrips overwinter on saved corms. You can discard corms after one year and buy new corms each year to avoid thrips, or you can treat your corms before storing, by dipping them in boiling water for 2 minutes to kill the thrips. Dry before storing. During the growing season, spray your gladiolus plants at first signs of damage with Neem oil or insecticidal soap to kill them.

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