How to grow gladioli

What you need to know about gladioli

Name: gladioli, sword lily, Gladiolus hybrids.

Height: 0.3–2m.

Foliage: simple, sword-shaped leaves with grooved ribs are arranged in a fan shape, arising from an underground corm.

Climate: grows well in warm to cool temperate zones as well as in tropical areas.

Soil: most well-drained soils are suitable.

Position: gladioli grow best in full sun with protection from strong winds.

Flowering and fruiting: attractive one-sided spikes of colourful, irregular funnel-shaped flowers in summer or early autumn.

Feeding: use a controlled-release organic fertiliser specifically for flowering plants at planting in winter or early spring. Liquid feed with a high potash fertiliser fortnightly just prior to, and during, flowering.

Watering: keep well-watered during the growing season. Allow them to dry out in late summer/early autumn once they have finished flowering and growing.

Appearance and characteristics of gladioli

Gladioli are perennials that grow from an underground corm, bearing sword-shaped leaves in a fan silhouette before producing a spike of striking, irregular, one-sided trumpet-shaped flowers in summer. The range of flower colours is extensive, and includes vibrant and pastel shades of white, pink, purple, red, yellow and orange that are often bi-coloured or ruffled. The large-flowered hybrids can grow up to 2m tall and make stunning cut flowers. Placed as a colourful highlight in a mixed border, gladioli may require some form of support for the flower stems. The smaller-flowered species and lower-growing cultivars and species make perfect easy-care container or edging plants.

Gladioli belong to the iris family and naturally occur in South Africa, tropical regions of Africa, Mediterranean Europe, the Middle East and Asia. There are around 300 different species of gladioli that can be found in varied environments, including rocky and sandy upland and coastal locations, rock ledges beside tropical waterfalls and fire-prone low scrubland. Gladioli are easy to grow in Australia’s warm temperate climate when positioned in full sun and protected from strong winds. They can usually be left in the ground over winter, but in areas with frosts or wet winters the corms are best lifted after flowering. Wait until the leaves yellow and die back, then lift them and wash and dry them before storing them over winter in a cool, frost-free environment. In marginal areas, cover the soil with a 5–10cm layer of compost or straw in late autumn.

The large-flowered hybrids (Grandiflorus group) are best lifted in autumn for improved flowering. All varieties of gladioli can successfully be grown in medium to large pots and containers, but the miniature butterfly hybrids (Nanus group) and the Primulinus group are better suited to this, due their smaller size and pleasing fragrance.

Uses for gladioli

Gladioli suit both natural and cottage-style planting, and can be planted as a background in mixed borders, as fillers after the spring bulbs, or used as edging along pathways.

How to plant and grow gladioli

When to plant gladioli

Plant the corms from winter to early spring in most temperate frost-free climates, or wait until early spring in cooler areas. Gladioli can be planted all year round in tropical climates, providing constant colour to the garden.

How to plant gladioli

1. Place the flat corms with the growing point facing upwards 10–12cm deep from the top of the corm to the soil surface and 10–15cm apart.
2. As a general rule, plant them around four times the depth of the corm.
3. Plant the corms in groups of at least 6–12 for the best overall effect, and water them in after planting.
4. Gladioli flower around 90–100 days after planting, so stagger the planting over fortnightly or monthly intervals to ensure a prolonged spectacular display.

Soil

Gladioli will grow in most well-drained garden soils. Incorporate some compost or aged manure before planting to retain moisture and to improve the soil. A pH between 6 and 7, which can be easily monitored with a pH kit, is preferred.

Always use a premium standard potting mix when planting gladioli in pots and containers, and keep them well-watered throughout summer.

Caring for gladioli

Fertiliser

Apply a controlled-release organic fertiliser specifically for flowering plants, underneath the corms at planting in winter or early spring. Liquid feed with a high potash fertiliser fortnightly, just before and during flowering, to build up the corms’ reserves for flowering next year.

How to prune gladioli

1. Remove spent flowers to build up the corms’ reserves and to stop some of the species from self-seeding in the garden or into natural areas, where some have become bushland weeds.
2. After flowering, the leaves and stems can be left to yellow off in late summer/early autumn.
3. If lifting them for storing, remove and discard the leaves and the old shrivelled corm below the new corm. Save this for planting next year.
4. Allow the corms to dry off completely.
5. When picking the flowers for a vase indoors, wait until the lowest flowers are open before cutting.

Diseases and pests

Aphids, thrips, snails and slugs can occasionally attack gladioli. Thrips are tiny brown to black ant-like insects about 1mm in length that hide and feed in the developing flower buds. This may cause the flowers to be damaged or fail to open. Aphids and thrips can be controlled with a safe insecticide applied prior to flowering. Iron chelate-based snail pellets can be applied around the plants to protect them from snail and slug damage during moist or wet conditions. Organic control methods include hand-picking, beer traps, and barriers of sawdust, crushed eggshells, wood ash or wood shavings.

How to propagate gladioli

Gladiolus can be easily increased by dividing up the clump of corms in late summer/autumn, when lifting the corms before storing them for winter. Remove the smaller cormels (tiny corms or cormlets) and store them over winter before replanting them the following spring. The larger corms will flower the following year, but the smaller cormels may take another 2–3 years to reach flowering size.

The species gladioli may be propagated by seed sown in spring.

If you like this then try

Canna: an exotic perennial with vibrant-coloured foliage and bold, flamboyant flowers throughout the summer months.

Daffodils: the classic spring bulb, daffodils mark the incoming sunny seasons with their golden yellow petticoat-like blooms in single or bi-coloured forms.

Foxglove (Digitalis): statuesque biennials and perennials with spikes of delicate two-lipped tubular flowers in spring.

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