How to Grow Gladiolus

Gladiolus Flowers

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If your previous exposure to gladiolus plants consists of a few stalks leaning this way and that in the flower garden, give this summer bulb, technically called a corm, a second chance. A mass of two dozen or more gladioli in bloom creates a garden spectacle of spiky blossoms, with some left over for your floral arrangements.

A member of the Iridaceae family, plants in the genus Gladiolus also go by the name flag flower and sword lily. Fast-growing gladiolus plants are a smart choice for gardens where space is a premium; they grow to from 2-5 feet tall, adding drama to the border.

Botanical Name Gladiolus palustris
Common Name Gladioulus
Plant Type Corm, or bulbotumer
Mature Size 2-5 feet
Sun Exposure Full sun
Soil Type Sandy loam
Soil ph 6.0-6.5
Bloom Time June through frost
Flower Color Red, pink, yellow, purple, green, orange, and white
Hardiness Zones 7-10 (USDA)
Native Area South Africa and Europe
Toxicity Toxic to humans, livestock, and pets

Gladiolus Care

Gladiolus plants produce trumpet-shaped flowers that open from bottom to top on a sword-like stem, adding drama to the landscape and bouquets alike. Hybridizers have expanded the color palette so that few flowers rival it, short of bearded irises. One color you won't find in the glad flowerbed is true blue, although plant purveyors try to persuade consumers with lavender plants bearing monikers like "Blue Moon." Many modern varieties have ruffled or frilled petals, adding to their appeal.

As annuals, the root system is limited, giving it a small footprint for the vertical accent these plants deliver. Even balcony gardens can accommodate a dozen gladiolus corms in a container. 

Move over, cosmos: Gladiolus flowers make excellent vegetable garden companions. The flowers attract pollinating insects to increase those tomato yields, and the bold blossom colors won't get lost between your rows of beans and squash. Plant gladiolus corms in the gaps where you've yanked out faded spring veggies like peas and lettuce. 

Gladioli look ungainly when they aren’t in bloom, but you can hide their awkward phase in the flower garden.  Another strategy is to plant glads behind medium to tall plants that will come into bloom when the glads are finished, like zinnias or dahlias.

Keep your glads off the ground by staking them with half-round plant stakes, hoop stakes, or single stem supports, depending on how many glads are in your grouping.

Light

Gladiolus do best in full sun, but if it's not available they will still flower in partial shade.

Soil

Any well-draining soil is fine for growing gladiolus bulbs. Although glads can tolerate shallow planting, placing them at least 6 inches under the soil’s surface provides support to emerging shoots.

Water

After initial planting, water well. Then, water gladiolus weekly.

Temperature and Humidity

Planting glads too early won’t reward you with earlier blooms: Gladioli pout in cold soil, and may even rot. Wait until night temperatures reach 60 degrees Fahrenheit before you set out your gladiolus bulbs, choosing a spot in your garden that receives at least five hours of full sun each day. Gladioli bloom from July until frost. However, the plants don’t bloom continuously, so planting new corms every two weeks will extend the blooming season.

Fertilizer

Fertilize newly emerged gladioli shoots with a balanced, 10-10-10 liquid fertilizer.

Are Gladiolus Toxic?

While people add colorful gladiolus flowers to salads, its bulbs, or corms, are poisonous to people, livestock, and pets.

Symptoms of Poisoning

Humans who ingest gladiolus corms may have mild stomach upset. Livestock and pets may experience nausea, diarrhea, salivation, and lethargy. Call your veterinarian immediately if the animals in your care have consumed corms.

Gladiolus Varieties

  • 'Atom': Red with picotee white border
  • 'Boone': Yellow with coral accents; said to be hardy to zone 6
  • 'Green Lace': Ruffled chartreuse blooms
  • 'Lucky Star': Unusual for its fragrance; white with red throats

Pruning

Pinch back dead flowers after they wither. When plant is done blooming, cut back the bloom with gardening shears to ground level unless you plan to dig and store your bulbs. 

Propagating Gladiolus

Start with premium sized gladiolus corms, which produce more blooms on heftier stalks. While you can get bargain bags of 10 centimeters glads for a reduced price, springing for 14-centimeter corms is a necessary first chapter of your gladiolus love story.  If the weather is dry at planting time, you can water the bulbs once, but don’t water them again until you see shoots or you may encourage rot.

Overwintering

Gladiolus flowers may perennialize in zone 8 and warmer, but most gardeners treat them as annuals. When first frost strikes, you can dig your glad bulbs for winter storage. Dry them for a few weeks, and store them in a cool, dry place.

Common Pests/Diseases


Thrips
sometimes bother gladiolus plants. You may not see the tiny winged insects, but you’ll notice brown foliage tips and flecked foliage. Treat thrips with insect soap.