Gladioli, Gladiolus

There's a huge range of gladioli that produce tall, upright stems, often with flowers ranged one above the other. All create splendid clumps of flowers in fantastic pinks, reds, oranges and other hot colours.

Recommended varieties

Tender, large-flowered gladioli are relatively recent hybrids. Southern European species, such as G. communis , have been grown since the 17th century, but the modern gladiolus didn't begin to take shape until the end of the 19th century.

Much of the breeding programme, using colourful South African species, was carried out in Europe and America, and today's plants bear little relation to their wild origins. Gladioli are available in almost every colour and hue, with flowers from 5cm to 18cm (2in to 7in) wide. Often there's a contrasting colour in the centre of the flower and petals may be frilled or ruffled.

It's important to distinguish between tender gladioli, which can't be left in the ground over winter, and hardier kinds, which can. Also check flowering times - some appear in early summer, some later. Hardy varieties are readily available but the choice is relatively small. However, almost every specialist nursery seems to sell its own tender kind.

Hardy border gladioli

The following aren't as blowsy as some, but add plenty of colour and style:

G. communis subsp. byzantinus : the boldest and most familiar gladiolus species, producing a stunning flash of rich magenta flowers in early summer. Known as 'Whistling Jack' in Cornwall, where it has become naturalised, it seeds freely in light soil and can spread. Has been given the Award of Garden Merit (AGM) by the Royal Horticultural Society (RHS).
G. papilio : the curved spikes of these narrow, hooded flowers are an unusual mix of greenish-yellow overlaid with purple. Blooms appear sporadically during late summer and autumn. Not completely hardy, so needs protecting over winter.

Scented gladioli

These don't have a knock-out scent, but get your nose right in and you'll get a fine whiff.

G. callianthus : one of the most beautiful gladioli, with large, scented white flowers, each with a beautiful maroon blotch in the centre ( G. murielae is very similar). It can be grown outside over summer, but often there's insufficient time after flowering for the corms to mature for the following year. Consequently, many treat it as an annual and grow it fresh each year in border groups or pots.

Modern hybrids

These come in three groups: Grandiflorus (also called florists' gladioli) are divided by flower size into giant, large, medium, small or miniature, and flower from early to late summer, as do gladioli of the Primulinus group. Plants belonging to the Nanus group flower in early summer.

G. 'The Bride': popular, delicate white flower that blooms from early spring to summer and won't grow above waist height. Has been awarded the RHS AGM.
G. 'Green Woodpecker': the ruffled greenish-yellow flowers have a red mark in the throat and open through mid and late summer. At 1.5m (5ft) high, best suited to the back of the border.
G . 'Prins Claus': clear white, early summer flowers with pink markings on 70cm (28in) stems.
G. 'Stromboli': large rich, red flowers in mid-summer on 1.5m (5ft) stems.
G. 'White City': medium-size ruffled white flowers open in the second half of summer on 1m (3ft) stems.

Growing tips

Site and soil preferences

All gladioli like rich, free-draining soil in a sunny, sheltered position, such as the foot of a south-facing wall or in a walled gravel garden. Plant in clumps of five to seven corms, 10cm (4in) deep and 10cm (4in) apart, during March and April. Mark the planting position with a small cane that can be replaced with a stake as required. Lighten heavy clay soils with well-rotted manure or compost. Plant each corm on a layer of sand to improve drainage.

Planting associations

'The Bride' is short enough to be tucked into the front of a border, while the pink varieties look good against silver shrubs or at the foot of a ceanothus. Big, showy hybrid cultivars can be mixed with other bedding plants, such as dahlias, which tend to flower at the same time and soften the gladioli spikes with their often large, round blooms.

Antirrhinums and petunias also make suitable companions, especially as all can be planted at the same time. Gladioli can also be planted in border gaps to add a touch of colour in late summer after the early flowering herbaceous plants have faded.

Aftercare

Gladioli need a regular supply of water when the buds begin to appear. After flowering, remove the flower stem but leave the foliage to continue growing into autumn as it feeds the bulb.

In late autumn, lift the corms and dry them off. Once dry, remove all soil and dead foliage. Store in a single layer in a frost-free shed or garage. Good ventilation reduces the risk of mildew.

Each corm will produce a number of smaller offsets. These take two years to reach flowering size and can be stored in the same way before being planted.