How to Grow Gladioli in Australia

Gladioli (Gladiolus hybrids) are summer-flowering perennials in the iris family (Iridaceae), grown for tall spikes of funnel-shaped flowers in beds and vases. The garden hybrids come mainly from South African species. Rows of 'gladdies' are grown for their corms on a farm near Bordertown, South Australia. The usual stumbles are corms planted too shallow and soil that stays wet.

Three mistakes that matter

1. Planting too shallow. A corm (a swollen underground stem base that stores food) set too shallow gives a spike that leans in wind. It also makes small corms for next year. Plant at the depth given under Planting Corms.
2. Planting into soggy ground. Corms that sit in cold, wet soil rot before they shoot or soon after. Choose free-draining soil, raise the bed on heavy clay, or grow in pots.
3. Cutting the leaves with the flowers. The leaves feed the new corm that forms on top of the old one. Take as little foliage as you can when picking, and let the rest yellow before lifting or tidying.

When to plant

Plant large-flowered gladioli once the risk of frost has passed, or from midwinter in frost-free gardens. Flowers usually follow 90 to 120 days after planting, sooner in warm weather. For a long run of spikes, plant a few corms every two to four weeks through the window.

Baby gladioli are the exception: plant them in autumn to early winter for flowers in late spring. In frosty districts, finish the last planting early enough for spikes to open before autumn frosts.

Site, soil and setup

Sun and drainage decide most of the result. Gladioli are not fussy about soil type, but they will not stand wet feet for long.

See soil pH explained before liming, and waterlogged soil if water lies on the bed after rain.

Garden gladioli or wild gladiolus?

The corms the store sells are garden hybrids. Two wild South African species have escaped gardens and now invade bushland. Wild gladiolus (Gladiolus undulatus) has creamy, wavy-tipped flowers and spreads across southern Australia. Pink gladiolus (Gladiolus caryophyllaceus) is common in Perth's banksia woodland. Both spread by tiny cormlets carried in dumped garden waste and soil.

Garden hybrids make cormlets too, so bin spent plants and spare cormlets rather than tipping them over the back fence.

Container growing

Any gladiolus grows in a pot, but the compact Glamourglad mix and baby gladioli suit pots best. Tall types need a pot at least 40 cm wide, about 27 L, to stop them toppling. Baby gladioli need a pot at least 20 cm deep, about 4.5 L for a 20 cm pot. Use premium potting mix, and set corms closer than in the ground.

• Watering. Keep the mix just damp until shoots show, then check daily in warm weather. See watering pots through summer.
• Feeding. Give fish and seaweed blend at 25 mL per 9 L every fortnight, then switch to liquid potash at the label rate once spikes appear.
• Position. Full sun, out of wind, on a level surface where a tall pot cannot blow over.
• After flowering. Keep watering until the leaves yellow, then let the pot dry off.

Planting Corms

Gladioli grow from dormant corms planted straight into their flowering spot.

Choosing a type

Planting direct

• Choose large, firm corms with no soft or discoloured patches, as bigger corms give bigger spikes.
• Set each corm flat side down, pointed tip up.
• Plant large-flowered types 10 to 15 cm deep and baby gladioli 8 to 10 cm deep. Go a little deeper in light, sandy soil.
• Space corms 10 to 15 cm apart, in clumps of six to twelve.
• Push in stakes now, beside the corms, so they never pierce one later.
• Water in well once, then keep the soil only just moist until shoots appear.

Care by growth stage

Gladioli need little feeding, because the corm carries the early growth. Steady water and a potassium feed as the spike forms do more than extra nitrogen.

Tie each stem loosely to its stake as it grows; one stake can hold three or four stems in a clump. A horizontal mesh of wire over a cutting row does the same job.

Where frosts are heavy or winters wet, lift corms once the leaves yellow. In mild, well-drained gardens they can stay in the ground for years under a 5 to 10 cm autumn mulch.

• Lift with a garden fork in dry weather, about six weeks after flowering, taking care not to stab the corms. Grey mould on the tops infects corms at digging, and damp weather favours it.
• Cut the leaves off a few centimetres above the corm, binning the tops if thrips were about.
• Dry the corms on a wire rack in an airy spot for two weeks.
• Twist off the old, shrivelled corm beneath the new one, and save cormlets if you want more plants.
• Store in net bags somewhere cool, dark and dry, at about 4 to 10°C.
• Check now and then for aphids and soft corms, and discard any that rot.

Keep stored corms out of reach of children, dogs and cats, as gladioli are toxic to pets and the corms hold the most toxin. Cormlets planted 5 cm deep usually reach flowering size in one to two years.

Companion planting

Lower, bushy plants in front hide the bare lower stems and leave the spikes the sun.

Grows well with

• Alyssum, a low edging whose flowers draw hoverflies, and hoverfly larvae eat aphids.
• Salvias, which share the full sun and fill the space around the base.
• Zinnias, sun-loving summer annuals that stay below the spikes.

Keep them apart from beans and peas, which host the bean yellow mosaic virus that aphids carry to gladioli.

Keep apart

• Beans and peas, hosts of bean yellow mosaic virus.
• Dense groundcovers, which hold damp around the corms and crowd new shoots.

Harvesting Blooms

Cut a spike when the lowest one or two flowers show colour or the first one opens; the rest open upward in the vase.

• Cut with a sharp knife or secateurs above the second to fourth leaf (see Three mistakes that matter).
• Stand stems straight into a bucket of clean water.
• Keep cut spikes upright; laid flat, the tips bend up towards the light.
• Snap off spent spikes left in the garden, which stops seed setting and builds the corm.

Cut gladioli are sensitive to ethylene, so keep the vase away from a bowl of ripening fruit.

Common problems

No flowers, only leaves. Small corms, too much shade or a crowded clump are the usual causes. Plant large corms in full sun, and lift and divide old clumps every four to five years.

Spikes leaning or falling. Shallow planting and wind are to blame (see Three mistakes that matter). Stake early and tie as the spike grows.

Corms that never come up. Cold, waterlogged soil rots them (see Three mistakes that matter). Dig one up: a firm corm is waiting for warmth, a soft one has rotted. Read more

Scorched or streaked flowers in hot spells. Extreme heat can mark petals much as thrips do. Check inside a bud for tiny insects before blaming the weather.

Pests and diseases

Thrips and aphids cause most of the trouble, and aphids spread the viruses that follow.

Gladiolus thrips (Thrips simplex). Tiny brown insects feed inside buds and on leaves, leaving white flecks, and badly hit buds fail to open. Females also lay eggs in corms, which carry the pest into the next season. Rinse leaves, undersides too, and keep stored corms below 10°C, where thrips stop breeding. Read more

Aphids (Aphididae). Small sap-suckers cluster on young leaves and also feed on stored corms. Hose off small colonies, and let hoverflies do the rest (see Companion planting). Read more

Mosaic viruses (bean yellow mosaic virus and cucumber mosaic virus). Leaves show pale yellow mottling and coloured flowers show streaks or broken colour. There is no cure, so pull and bin infected plants. Read more

Fusarium corm rot (Fusarium oxysporum). Leaves bend down, yellow and die early, and corms rot brown from the base upward. The fungus lives in soil for years and favours warm conditions, so bin infected corms.

Bacterial scab (Burkholderia gladioli). Round, sunken brown spots with a shiny, varnish-like crust mark the corms, worst in heavy, wet soil. It survives on corms and in soil, so discard marked corms and rest the bed (see Site, soil and setup).

Garden snail (Cornu aspersum). Snails and slugs chew new shoots and leaves at night, mostly in wet weather. Pick them off by torchlight after rain. Read more

Prevention first

• Plant virus-tested corms where you can, because a firm, healthy-looking corm can still carry a virus.
• Water at soil level rather than over the leaves, which helps keep fungal disease down.
• Control aphids early, because viruses travel with them.
• Keep the bed weeded and clean up spent tops, which shelter thrips and disease. See garden hygiene.

Tips

1. Set the near-black 'Black Sea' or deep crimson 'Espresso' beside the lime-green 'Green Star' or white and pink 'Priscilla', so each colour stands out.
2. Plant baby gladioli in an old wire hanging basket sunk into the bed, so the small corms are easy to find and lift.
3. Label net bags of stored corms by variety, so colours go back where you planned them.
4. Grow a short row in a spare vegie patch bed purely for cutting, and the border keeps its flowers.

Due to quarantine restrictions and our shipping policy, we cannot send gladioli corms to Western Australia or Tasmania.