Gladiolus is a summertime favorite, with tall spikes of flowers that come in almost every color except true blue. Also called sword lilies, gladioli are easy to grow and available with plain, ruffled or frilly blooms. Most are hardy to USDA Zone 7, although the nanus species is a hardy gladiolus that overwinters to Zone 5.
I. Appearance and CharacteristicsÂ
Gladiolus (from Latin, the diminutive of gladius, a sword) is a genus of perennial cormous flowering plants in the iris family (Iridaceae).
It is sometimes called the ‘sword lily’, but is usually called by its generic name (plural gladioli).
The genus occurs in Asia, Mediterranean Europe, South Africa, and tropical Africa. The center of diversity is in the Cape Floristic Region. The genera Acidanthera, Anomalesia, Homoglossum, and Oenostachys, formerly considered distinct, are now included in Gladiolus.
The South African species were originally pollinated by long-tongued anthophorini bees, but some changes in the pollination system have occurred, allowing pollination by sunbirds, noctuid and Hawk-moths, long-tongued flies and several others. In the temperate zones of Europe many of the hybrid large flowering sorts of gladiolus can be pollinated by small well-known wasps. Actually, they are not very good pollinators because of the large flowers of the plants and the small size of the wasps. Another insect in this zone which can try some of the nectar of the gladioli is the best-known European Hawk-moth Macroglossum stellatarum which usually pollinates many popular garden flowers like Petunia, Zinnia, Dianthus and others.
Gladioli grow from round, symmetrical corms (similar to crocuses) that are enveloped in several layers of brownish, fibrous tunics.
Their stems are generally unbranched, producing 1 to 9 narrow, sword-shaped, longitudinal grooved leaves, enclosed in a sheath. The lowest leaf is shortened to a cataphyll. The leaf blades can be plane or cruciform in cross section.
The flowers of unmodified wild species vary from very small to perhaps 40 mm across, and inflorescences bearing anything from one to several flowers. The spectacular giant flower spikes in commerce are the products of centuries of hybridisation and selection.
The flower spikes are large and one-sided, with secund, bisexual flowers, each subtended by 2 leathery, green bracts. The sepals and the petals are almost identical in appearance, and are termed tepals. They are united at their base into a tube-shaped structure. The dorsal tepal is the largest, arching over the three stamens. The outer three tepals are narrower. The perianth is funnel-shaped, with the stamens attached to its base. The style has three filiform, spoon-shaped branches, each expanding towards the apex.
The ovary is 3-locular with oblong or globose capsules, containing many, winged brown, longitudinally dehiscent seeds.
These flowers are variously coloured, ranging from pink to reddish or light purple with white, contrasting markings, or white to cream or orange to red.
II. How to Grow and Care
Sunlight
Gladiolus thrive in full sun. They will bloom in shade, but the flowers will be smaller, and the flower stalks will be floppy.
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.
Soil and Water
Well-drained soil is essential for this plant to thrive. If your soil is filled with clay, is too wet, or is boggy, plant gladiolus in raised beds. The plants need 1 inch of water a week, slightly more if they are in raised beds, but don’t overwater them.
Fertilizing
When planting in spring, amend the soil with compost. Add a balanced, water-soluble fertilizer when the plants reach 10 inches high and again when the flowers start to show their color, following the product instructions.
Planting Instructions
Begin planting gladiolus corms in spring, two weeks before the last expected frost date.
Be sure to plant the pointed side of the corms up, about four times as deep as their width. Space the glad corms 6 to 8 inches apart. If you are planting gladiolus in a garden bed, plant in drifts of at least seven bulbs for a pleasing display. Spread a 2-inch layer of mulch on the soil surface and water the newly planted corms well. Leaf stalks will emerge in a couple of weeks.
Harvest bouquets of glads for six weeks or more in summer by staggering the planting of corms. Plant a group every two weeks in spring. Stop planting in mid-June to give the plants plenty of time to mature before a damaging freeze in fall. When planting long rows of corms to use as cut flowers, plan to stake each stem along one side of the row, tying the stems to the plants they grow.
Pruning
Gladiola don’t require pruning. They are grown as annuals or as cut flowers. In areas where they overwinter in the ground, deadhead the flower stalks after their blooms are spent to prevent self-seeding. Cut back the remaining foliage for the winter.
Propagation
Propagate gladiolus by dividing corms or via harvesting seeds.
- Division
Dig up gladiolus corms for storage at the end of the season. Each corm will have several baby corms called cormlets attached to it. Carefully remove the cormlets, store them over the winter in a dry place, and plant them separately in spring. They will grow a plant the first year but not produce a flower. Dig them up in the fall and store them over the winter as you do your other gladiolus corms. Replant them in spring, and they will reach flowering size during the second year.
- Seeds
To harvest seeds from gladiolus, leave the flowers on the stalks for about six weeks after they die and recover the hard casing that is filled with seeds. Open the casing to remove the seeds. Store them in a cool, dry place. In spring, sow one seed each in 4-inch pots filled with potting soil. Barely cover the seed, water the pot, and cover it with plastic. When the seed sprouts, remove the plastic and move the pot to a sunny spot. Grow the plant outdoors in its pot for the first year, harvest the tiny cormlet it produces, and store it for the winter. For the next two years, plant the cormlet outdoors and dig it up to store for winter. By the third year, it will reach flowering size.
Pests and Diseases
The best way to avoid problems with gladiolus corms is to plant only healthy corms. Discard any that are damaged or soft.
Thrips are the main pest of gladiolus. They feed on the flowers and leaves. Spray the plants at the first sign of damage with insecticidal soap or neem oil.
If the spot your gladiolus is planted in is too wet or soggy, corms may rot or grow mold, viruses, or bacteria that can prevent growth or flowering. Choose a site with well-drained soil and plant undamaged corms.
In growing zones 6 and colder, corms may not be able to survive winter outdoors. Dig up corms in the fall and store them indoors in a cool, dark, dry place, then replant in fall.
Potting and RepottingÂ
Gladiolus is an excellent container plant. Fill a large deep pot that has drainage holes with well-draining potting soil amended with compost, spacing the corms about 2-3 inches deep and 4 inches apart. Move it to any part of the garden that needs a pop of color. Prepare other pots a month apart for continuous color all summer and into fall.
Keep the pot in a sheltered spot for the winter, and the gladiolus will bloom again the following year, or remove newly formed corms for propagation purposes and repot each year.
Overwintering
Gladiolus flowers may perennialize in zone 8 and warmer, but most gardeners treat them as annuals. When the 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.
III. Uses and BenefitsÂ
Gladioli have been extensively hybridized and a wide range of ornamental flower colours are available from the many varieties. They can make very good cut flowers for display.
Gladioli are used as food plants by the larvae of some Lepidoptera species including the Large Yellow Underwing, and gladiolus thrips.
IV. Harvesting and Storage
- Harvesting
To ensure that your cut flowers will last, cut the flower spikes when only one or two blossoms are open. The remainder of the buds will follow in the first bloom’s footsteps. Immediately plunge the stems in lukewarm water. As lower flowers fade, pull them off and cut about an inch of the stem off the bottom of each spike every few days.
- StoringÂ
In Zones 7 and colder, glad corms can be dug up in the fall and stored for planting back in the garden in springtime. Once a harsh frost kills gladiolus foliage, dig up the corms. Shake off excess soil and place the corms in a warm, dry, airy place for about three weeks. Make sure to get rid of any shriveled, old, spent corms, placing the healthy bulbs in a paper sack to store in a cool and dry place until spring. Many gardeners choose not to dig and store glads; they purchase new corms each year. The choice is yours!
