Gladiolus

Fundamental Facts

HARDINESS: Zones 5 to 10
PREFERRED SOIL pH: Neutral
PREFERRED SOIL TYPE: Average
PREFERRED LIGHT: Sun
ATTRIBUTES: Tall spikes of dramatic flowers in many colors; for beds, cutting
SEASON OF INTEREST: Late spring to summer
FAVORITES: Choose hybrids by color; G. x cohrillei, G. communis ssp. byzantinus
QUIRKS: In warm climates, corms can overpopulate if left in the ground over winter
GOOD NEIGHBORS: Celosia, gomphrena, lavatera, marigold, zinnia
WHERE IT GROWS BEST: In sunny, well-drained sites protected from wind
POTENTIAL PROBLEMS: Thrips; root rot in overly wet soil
RENEWING PLANTS: Lives many years; divide overgrown clumps
CRITTER RESISTANCE: Good
PLANTING DEPTH: 4-6 in (10.2-15.2 cm)
SOURCE: Corms
DIMENSIONS: Hybrids to 4 ft (1.2 m) tall; hardy types 2-3 ft (0.6-1 m) tall; flowers to 4 in (10.2 cm) wide

Gladiolus in the Landscape

Topping out at 4 ft (1.2 m), with bold, colorful spikes of funnel-shaped flowers atop leaf blades, gladiolus are like exclamation points for the garden. These inexpensive, easy-to-grow bulbs bloom in lovely colors and
bicolors ranging from pure white to dark red and provide outstanding cut flowers for summer bouquets. Cut gladiolus when the first flowers at the bottom of the spike are open; the others will quickly unfurl in the vase.
Because of their lanky physique, glads can be awkward in the landscape. For the best effect, grow them in groups at the back of the border or station the tall spires against a fence or building, letting the structure act as a backdrop while blocking wind and helping to support the plants.

All in the Family

The common summer-flowering gladiolus are hybrids that are usually hardy to Zone 9. But there are other types that withstand more cold. At only 2 ft (0.6 m) tall, Gladiolus x colvillei is an early-blooming glad that is hardy to Zone 7 and has bright red flowers with yellow blotches. G. communis ssp. byzantinus is hardy to Zone 5 and grows 2-3 ft (0.6-1 m), with purple-red flowers often striped in white. Plant hardy gladiolus in groups of 5 or more for a care-free display of color in late spring to summer.

Growing Gladiolus

Gladiolus bloom about 10 weeks after planting. By planting die corms every 2 weeks from early spring through midsummer, you'll enjoy a succession of blossoms all season. Choose a sunny, well-drained spot and mix an all-purpose granular fertilizer, such as 10-10-10 into the soil as you dig, allowing about 1 tablespoon of fertilizer per corm. Plant the corms 4-6 in (10.2-15.2 cm) deep and 4 in (10.2 cm) apart. The small nubbin of new growth indicates the top of the corm and should point up.

Gladiolus grow so tall and slender that they need to be planted in groups of 3 or more and staked with bamboo canes and some soft garden twine to inconspicuously "corset" the group. Water only if the soil becomes very dry, as gladiolus hate wet soil and can develop root rot. Provide plants with a second helping of balanced fertilizer when flower spikes appear. In midsummer, watch for signs of thrips. These nearly invisible, sap-sucking insects make silvery streaks in leaves and distort flowers. Control thrips with a commercial insecticide labeled for this use, as directed.

In areas where gladiolus are not hardy, dig the corms when the leaves begin to yellow in late summer and trim the leaves to 1 in (2.5 cm) from the corm. Brush away loose soil and store corms in a paper bag of peat moss in a cool, dry, dark place, such as an unheated room or a garage that remains above freezing. Many gardeners in warmer climate Zones dig and store the corms, too, to keep plants from growing small, weedy offspring called cormlets. Cormlets reach flowering size in about 3 years, but because the mature corms are inexpensive, there is little reason to nurture cormlets.