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Gladioli

Folkert Siemens Folkert SiemensUlrike Hanninger Ulrike Hanninger

Gladioli not only decorate sunny flower beds in the garden, they also make excellent cut flowers. Here’s how to plant and care for them.

Origin

Gladioli (gladiolus), also known as Sword Lily, belongs to the Iris (Iridaceae) family. The Gladioli genus includes over 200 wild species which spread from Southern Europe to the Near East and Africa. The species with the most magnificent flowers originate from South Africa. Gladioli are strictly protected due to their rarity - today, they can only be found in a few locations on periodically wet moorland with humus-rich, calciferous soil. Due to their colorful, magnificent flowers, Gladioli are not only sought after as summer flowers in sunny beds, they are very popular as in a vases.

Appearance and Growth

While the wild species and types of Gladioli rarely grow taller than 24 inches, hybrids can grow up to 59 inches in good soils. All Gladioli have parallel-veined, sword-like leaves - which is also where they get their botanical genus name (in Latin, “gladius” means sword). They form bulbs as overwintering organs into which the flowers retract. They can survive in inhospitable environments, such as the South African steppes. The large flowers of this frost-sensitive bulbous plant appear from the end of June until September, depending on when they are planted. They appear on spikey inflorescences and have an irregular structure with just one, vertical symmetry level. There are Gladioli varieties in almost every flower color, from white to green and yellow, orange, red, violet to smokey gray and brown.

Location and Soil

Gladioli prefer deep, permeable soil. The substrate should be fresh to slightly moist and very nutrient-rich. A drainage layer of coarse sand is essential in heavy impermeable soils. Furthermore, Gladioli are true sun worshippers and should certainly have a sunny and protected spot in the garden.

Marsh Gladiolus (Gladiolus palustris)

Planting

Gladioli should be planted at the end of April, at the earliest, to ensure their frost-sensitive shoots only come to the surface after the frosts. If you want flowers earlier, Gladioli can also be cultivated in pots and, after the frosts have finished, in flower beds. Ensure that the layer of soil on top of the bulb is at least twice as deep as the diameter - this is the only way to ensure the tall growing flower stem is sufficiently sturdy. Bulbs can be planted from the end of April until the end of May, with a delay of a week between planting each one, in order to extend the flowering period. Be aware that, similarly to Roses, Gladioli should only be planted in the same location every six years.

Care Tips

A good supply of nutrients is one of the most important care tips for Gladioli. As Gladioli require lots of nutrients, the planting location should be sprinkled with mature compost and horn meal as soon as the bulbs have been planted. Gladioli can be cut as soon as the first flower or two have opened. Take care to always leave four or five leaves on the plant to that a new bulb can develop. Cut withered inflorescences early to prevent seeds from forming.

Overwintering

To overwinter Gladioli, dig up the bulbs in the fall after the first night frost, shake of any larger clumps of soil and place them in a wooden box with course sand. A cool, frost-free basement with high humidity levels is the perfect winter storage space.

Overwintering Gladioli

The frost-sensitive Gladioli must be dug up and stored before the winter

Utilization

Gladioli, similarly to Dahlias, are popular bulbous plants which were previously ubiquitous in cottage gardens. They can be integrated into any flower or shrub bed, provided the location is sunny and the soil is very permeable. Gladioli are perfect for narrow planting strips in the house and on the patio as they require very little space.

The wild species are happy in rock gardens or marshy areas around garden ponds, depending on their preferred environment. Gladioli can also be integrated into modern designs, however the small flowering botanical species and varieties are preferable here. Gladioli and Butterfly Gladioli can also be readily cultivated in containers and make superb cut flowers. Always plant Gladioli in small and larger groups of 5 to 15 bulbs. If possible, choose shade in shade combinations or select two color coordinated flowers, otherwise the bed will quickly become too colorful.

Gladioli as cut flowers

Gladioli look fantastic as cut flowers in vases

Important Species and Varieties

Numerous garden hybrids have resulted from cross-breeding various wild species; this are generally listed under the botanical name Gladiolus x hortulanus. You can generally tell the difference between single-color Gladioli and Butterfly Gladioli from the flowers, as well as the Baby and Wild Gladioli, which are largely species and varieties which are small-growing with few breeding differences.

One beautiful Butterfly Gladiolus is the variety “Blackpool”, which has yellow flowers with red flecks. ‘Lady Godiva’ is white with a green pattern. Of the small-growing varieties, which reach a maximum height of 20 inches, ‘Nymph’ (white and red flecks), ‘Guernsey Glory’ (dark violet, red tips and white flecks) and ‘Atom’ (red with white edges) are all well established.

Propagation

Division is the simplest and most successful method for propagating Gladioli. Most varieties readily form side bulbs in loose soils; these are generally connected to the mother bulb with short offshoots. Separate them by simply taking them from the plant in the fall, ideally planting the small bulbs in coarse and cultivating them over the winter in a bright, frost-free spot. The wild species can also be propagated by sowing seeds - however, it takes a few years until they flower for the first time.

Diseases and Pests

In heavy, moist soils and cold, wet weather in particular, Gladioli tend to develop bulb and stem rot which can be caused by various fungal pathogens, such as Fusarium and Sclerotina. Certain bacteria can also trigger these plant diseases. Leaf spots can also occur. Gladioli experts recommend immediately removing affected plants and subjecting the other bulbs to a half-hour hot water treatment at 127 degrees Fahrenheit when overwintering, in order to kill possible pathogens. Then place them in cold water for a few minutes and leave them to dry out thoroughly before overwintering.

Frequently Asked Questions

When can Gladioli be planted?

Gladioli should be planted at the end of April at the earliest. This means the frost-sensitive shoots only appear at the surface after the frosts have finished. You can extend the flowering time by planting the bulbs at periodic intervals between the end of April and the end of May.

What type of soil is suitable for Gladioli?

Gladioli require permeable, sandy-loamy and extremely nutrient-rich soil. Keep the substrate fresh to slightly moist.

Are Gladioli winter-hardy?

Most Gladioli are extremely frost-sensitive. To overwinter Gladioli, dig up the bulbs and store them in the fall. In mild winter regions, the bulb plants can also stay outside with winter protection.

Are Gladioli poisonous?

Gladioli are not poisonous. However, sensitive people should take the precautionary measure of wearing gloves in cases of intensive contact.

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