Gladioli: to plant, to grow and to maintain

Botany

The gladiolus is a perennial plant with between 270 and 300 botanical species, and over 10,000 horticultural varieties. The majority of species originate from South Africa. Others grow in other regions of Africa, in western Asia, or around the Mediterranean. The centre of diversity for gladioli is the floral region of the Cape in South Africa. In France, there are 7 species found in the wild, including Gladiolus italicus and Gladiolus byzantinus, two species sometimes introduced into gardens. Gladioli have been widely spread by humans around the world for cultivation. Gladioli are divided into three main groups: grandiflorus, nanus, and primulinus.

It was in the 18^th century that gladioli from South Africa were imported to Europe for cultivation. Hybridisation began in the early 19^th century. The horticultural varieties found today in gardens are derived from 6 or 7 South African species.

The gladiolus belongs to the family Iridaceae, like irises and crocuses! This family contains between 1,800 and 2,000 species, among which many plants are cultivated for their aesthetic appeal: crocosmia, chasmanthe, dierama, dietes, freesia, ixia, tritonia… These are monocotyledonous plants, often herbaceous, and generally have underground storage organs: bulbs, corms, rhizomes… Most of the time, their leaves are linear, thick, upright, and have parallel veins.

Gladiolus grandiflorus: botanical illustration

The name gladiolus comes from the Latin gladius, meaning sword, alluding to the shape of the foliage, slender, upright, and pointed. It is a plant that symbolises strength and victory, heroism. In Roman times, gladiolus flowers were offered to gladiators who won a fight.

Gladioli have an elegant, very elongated shape. They bring verticality and dynamism to the garden. They are generally quite tall; thus, they are usually placed in the middle or back of flower beds to accompany smaller plants. The tallest varieties can reach 1.50 m, even 1.80 m. Conversely, there are dwarf gladioli (Gladiolus nanus, Gladiolus colvillei, Gladiolus illyricus…) that do not exceed 50 cm in height.

Gladioli have a rigid, very upright appearance. Their stems are quite thick and are generally not branched. Their lack of flexibility makes them quite sensitive to wind. This explains why the tallest varieties need staking.

The gladiolus blooms in summer, between June and September-October, for about 15 days, sometimes longer. The flowering period also depends on when you planted them, which is why it is advisable to stagger the plantings. Gladioli generally bloom two and a half to three months after planting. There are also gladioli that bloom in spring, such as Gladiolus byzantinus. Dwarf gladioli, Gladiolus nanus, usually bloom at the end of spring, around June.

The gladiolus offers a flowering in long, very upright and rigid spikes. They are composed of flowers grouped densely, all on one side of the flower stem. The spikes often bear between ten and twenty-five flowers – sometimes fewer in smaller gladioli (Gladiolus nanus, Gladiolus papilio, etc.). The flowers do not all open at the same time: those at the bottom open first, followed by those at the top.

Generally, gladiolus flowers are quite large. They have been specifically selected for their impressive flowering. Therefore, it is the large-flowered varieties (hybrids of Gladiolus grandiflorus) that are the most marketed and the most common in cultivation. The flowers of botanical species and butterfly gladioli are smaller. In general, gladiolus flowers often measure between 2 and 5 cm in diameter.

They have a funnel or trumpet shape. They are sometimes elongated and not fully open – the tepals forming a long, thin tube – as in Gladiolus italicus, but can also be fully open (Gladiolus callianthus). They are composed of smooth or undulated, frilled petals. Some gladioli have fine, slender petals, very elegant, giving them a lily-like appearance, as in the case of Gladiolus colvillei ‘The Bride’.

Gladioli offer diverse flowerings! From left to right, Gladiolus ‘Priscilla’ (photo Pharaoh Hound), Gladiolus papilio ‘Ruby Free’, Gladiolus ‘Carl Lewis’, Gladiolus byzantinus, Gladiolus callianthus (photo Leonora Enking)

Gladiolus flowers consist of six tepals (three petals and three sepals, having the same appearance). There are two bracts at the base of each flower. The tepals form a tube at the base. The central tepal, located above, is often the largest. It is topped by three stamens. The three outer tepals are generally smaller. The flowers are bisexual: they have male (stamens) and female (pistil) organs. The stamens are sometimes decorative, as in Gladiolus colvillei ‘The Bride’, where they are purplish and add nuance to the immaculate white flowering. The gladiolus flower is of type 3: there are three sepals, three petals, three stamens, and a style divided into three branches. Later, the capsules (fruit) will open in three parts.

While gladioli generally have a very rigid and imposing appearance, some species have much more delicate, lighter, and more flexible forms, as is often the case with botanical gladioli, particularly Gladiolus carryophyllaceus, Gladiolus papilio, or Gladiolus byzantinus.

Gladioli offer a very wide range of colours, as their flowers exist in almost every shade, from the softest to the brightest! Some varieties are striking, while others are more pastel, delicate… And there are also gladioli with a dark red hue that is almost black. However, true blue flower varieties are not really found.

The flowers can be solid-coloured, but they are sometimes shaded, with a lighter or darker throat. Butterfly gladioli generally have bicoloured flowers, with bright colour spots that evoke butterfly wings! Some varieties of Gladiolus nanus offer an original flowering, white with three or four oval pink markings on the petals on one side of the flower (Gladiolus nanus ‘Impressive’ or ‘Nymph’). In Gladiolus primulinus ‘Atom’, the petals are red but highlighted by a fine white edge on the border.

Gladiolus flowers are very often used as cut flowers for making bouquets! They have a good vase life (about 15 days).

The acidanthera, or Gladiolus callianthus, is appreciated for its fragrance!

The gladiolus has upright, elongated, fairly narrow leaves. They are sword-shaped, which gives the plant its name Gladiolus (from Gladius: sword). They measure between 20 and 60 cm in length. These are relatively characteristic leaves of the Iridaceae. They have parallel, longitudinal veins and are quite thick and leathery. The leaves emerge from the base and are arranged in a fan shape, sheathing.

The leaves of the gladiolus are green, sometimes slightly bluish.

The foliage is deciduous; it wilts in autumn. It is important to leave it in place until it dries out by itself, as it plays a crucial role in allowing the bulb to replenish its reserves. You can cut it once it is completely dry.

The foliage of gladioli (photo Wouter Koppen – iBulb)

The gladiolus has underground organs often referred to as “bulbs,” although they are actually corms. They are rounded and flattened, surrounded by a brown, fibrous tunic. This is the base of the stem that has swollen to accumulate nutrient reserves. The corm depletes during flowering, then produces another corm just above, which replaces the old one. The largest bulbs ensure the most beautiful blooms, the largest flowers. That is why we recommend choosing preferably large-calibre bulbs, at least 12 or 14. Around the corm, the gladiolus produces small bulblets, or bulbil, which can be detached and replanted elsewhere to multiply the plant… but they need several years to grow and be able to produce flowers.

The butterfly gladiolus, Gladiolus papilio, has underground stolons that allow it to spread.

The corms of gladioli (photo Wouter Koppen – iBulb)

The fruit of the gladiolus is a capsule that contains many brown, winged seeds (except for Gladiolus italicus, which has smooth seeds). When the capsules are ripe, they open in three parts.

The fruit of Gladiolus communis (photo Meneerke bloem) / The ripe fruit of Gladiolus italicus (photo Meneerke bloem) / The fruits and seeds of Gladiolus illyricus (photo Roger Culos – Museum Toulouse)

The gladiolus is not a fully hardy plant. It is better to dig up its corm in autumn to store it in a frost-free shelter. However, there are a few relatively hardy species: Gladiolus italicus, Gladiolus byzantinus, Gladiolus papilio…

The main varieties

The most popular varieties

Our favourite varieties

Other varieties to discover

Gladiolus callianthus - Abyssinian gladiolus

Also known as Acidanthera, this gladiolus bears elegant white flowers, marked with dark purple in the centre. The contrast is stunning, and the petals are finer than those of other gladioli. Additionally, the flowers are fragrant!

• Flowering time September to November
• Height at maturity 60 cm

See the product sheet

Gladiolus italicus - Italian Gladiolus

The Byzantine gladiolus offers delicate pink-violet flowering. The flowers are elongated, quite slender, and have a very natural appearance. Moreover, it is quite hardy! It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Flowering time May to August
• Height at maturity 60 cm

See the product sheet

Gladiolus White Prosperity - Sword Lily

A gladiolus that offers a beautiful flowering of immaculate white! Very elegant, it can find its place in a romantic garden or a cottage garden.

• Flowering time August to October
• Height at maturity 1,20 m

See the product sheet

 

 

Gladiolus primulinus Atom - Sword Lily

This variety offers a brilliant flowering, with bright red petals, accented by a fine white edge around the perimeter!

• Flowering time July to October
• Height at maturity 60 cm

See the product sheet

Gladiolus The Bride - Sword Lily

A very elegant flowering, with long and slender petals. The flowers are white, slightly marked with cream-yellow in the centre. The purple stamens are also decorative.

• Flowering time July
• Height at maturity 45 cm

See the product sheet

Gladiolus Violetta - Sword Lily

This gladiolus is appreciated for its large flowers of a deep, quite intense violet. The petals are highlighted by a white edge on their contour.

• Flowering time August to October
• Height at maturity 1 m

See the product sheet

Gladiolus Robinetta - Sword Lily

This is a dwarf gladiolus that offers a flowering of bright red! It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Flowering time August, September
• Height at maturity 50 cm

See the product sheet

 

 

Gladiolus Lorena - Sword Lily

This is a butterfly gladiolus. The flowers are white and accented by two lateral petals, red and yellow, evoking butterfly wings.

• Flowering time August to October
• Height at maturity 1 m

See the product sheet

Gladiolus Nymph - Sword Lily

The flowers of this variety are white, with the lower petals marked with pink-red macules... A flowering that is both delicate and original!

• Flowering time July, August
• Height at maturity 50 cm

See the product sheet

Gladiolus Espresso - Sword Lily

This gladiolus offers large flowers of a very intense red, with black and velvety reflections. A dark, sensual, and elegant flowering.

• Flowering time July to September
• Height at maturity 1,20 m

See the product sheet

Planting Gladioli

Where to plant?

Plant the gladiolus in full sun to ensure a beautiful flowering. They bloom less well when planted in the shade. In a garden in the south of France, however, they can be planted in partial shade if there is enough light.

Gladioli do not appreciate soils that retain water in winter, as the corms may rot: this is why it is important to grow them in a light and well-draining substrate. If your soil is clayey and compact, it will need to be improved by adding coarse sand or gravel. Gladioli prefer sandy soils. The Marsh Gladiolus, Gladiolus palustris, is an exception, as it thrives in moist soil.

The gladiolus appreciates fertile soils rich in organic matter. We recommend adding well-decomposed compost. However, avoid fertilising with manure as it may cause the corms to rot.

Place it preferably in a wind-protected location, as wind may damage the long flower spikes. If exposed to wind, it will require staking.

Gladioli are susceptible to several fungal diseases: to limit the risk of transmission, avoid replanting the bulbs in the same spot from one year to the next.

When to plant?

Gladioli are planted in spring, from April until May-June. In a mild climate, they can even be planted from March, while in colder regions it is better to wait until May. You can stagger the plantings by installing bulbs every two weeks.

Some species are planted in autumn, around September-October. This is the case for Gladiolus byzantinus and some spring-flowering gladioli.

How to plant gladioli?

For a more beautiful effect, it is preferable to plant gladioli in groups of at least 7 or 10 plants. You can also scatter them in a flowerbed for a fairly natural look. They are sometimes recommended to be planted in rows, especially when grown for cut flowers. In any case, maintain a distance of about 15 cm between each corm. You can use a bulb planter.

When purchasing your gladioli, we advise you to choose corms of at least size 12. Their flowers will be more beautiful.

1. Prepare the soil to loosen it, remove weeds, large stones, and break up clumps of earth. Optionally, add some well-decomposed compost.
2. Dig a hole. If your soil is heavy, you can add some coarse sand at the bottom for drainage.
3. Place the corm in the correct position (with the point facing upwards). It should be planted about ten centimetres deep.
4. We recommend planting a stake next to each bulb to support them once they grow tall. This will also serve as a marker to remember their location and avoid damaging the corms if you need to replant in the same flowerbed soon.
5. Cover the bulbs with soil and firm down.
6. You can water lightly if the weather is dry.

The gladioli will bloom two to three months later.

Also discover our advice sheet on planting gladioli! and 5 gladioli to grow in pots

Planting the gladiolus (photos Wouter Koppen – iBulb)

Maintenance

Water regularly during summer and throughout the flowering period. Water at the base to avoid wetting the leaves, as gladioli are susceptible to several fungal diseases that thrive in humidity. You can install a layer of mulch to keep the soil cool and prevent weeds from growing. It is not advisable to water when the plant is dormant or just beginning its growth. Wait until it has several leaves before starting to water. Gladioli dislike stagnant moisture, as this can cause the corms to rot.

You can take advantage of watering to provide some liquid fertiliser, especially in spring, possibly using a “bulb special” fertiliser. Avoid using manure as it may cause the bulbs to rot.

When the gladioli start to grow taller, you can set up discreet staking to support the flower spikes of the taller varieties, especially if they are exposed to wind.

We recommend regularly removing faded flowers and cutting the flower spikes once all the flowers have faded.

In any case, do not cut the leaves before they have completely dried. They allow the plant to replenish its reserves, storing nutrients in the corm before entering dormancy to be able to flower again the following year.

Feel free to pick the flowers to make bouquets! But in this case, cut while leaving the leaves in place, as they are important for the corm to replenish its reserves and flower again the following year. Let them fade and dry naturally.

Storing gladiolus corms in winter

If you live in a cold climate region where temperatures frequently drop below -10°C, you will need to dig up the bulbs in autumn to protect them from frost:

1. Wait until the foliage has turned yellow and dry, then dig up the corms, being careful not to damage them.
2. You can sort them and keep only the largest ones (these are the ones that produce the most beautiful flowers!)
3. Clean them by removing the soil, cutting the stem and leaves. Do not remove the corm’s skin.
4. Let them dry by placing them for several days in a warm, ventilated place.
5. Once they have dried, you can remove the old bulb each time, which is located just below the new one.
6. Place them in a box, on a layer of sand or sawdust, ensuring they do not touch each other.
7. Store them in a dark, dry, airy, and cool place (between 2 and 10°C).
8. You can replant them in spring.

Beware of rodents and mould during winter!

If you live in a mild climate region, feel free to leave the bulbs in the ground! Similarly, some gladioli are much hardier than others (Gladiolus papilio, Gladiolus nanus…). They can survive the winter in the ground. However, gladioli that remain in place for several years will become less and less floriferous over the years, as they produce bulblets each year that initially only produce leaves! It is better to renew the clumps from time to time.

Discover our advice sheet: Dividing, wintering, and multiplying gladioli

Diseases and pests of gladiolus

Gladiolus is sensitive to botrytis, a fungal disease characterised by the presence of a felt-like growth.

It can be affected by septoria (small brown spots on the leaves) and fusarium (the leaves dry out and turn yellow). Gladiolus can also be impacted by rust. To limit the risk of transmission of these diseases, avoid replanting gladiolus in the same location year after year (ideally wait at least four years before replanting gladiolus in the same spot). These diseases are also favoured by humidity: grow your gladiolus in well-draining soil, avoid excessive watering, and ensure that you do not wet the leaves when watering.

Gladiolus is sometimes attacked by aphids, which pierce the leaves and extract the sap from the plant. Treat with black soap to get rid of them. It can also happen that slugs nibble on the leaves. You can use ferramol or create a slug trap. Thrips also pose a problem for gladiolus cultivation, causing discoloured spots to appear on the flowers or leaves. They can lead to flower deformation or prevent them from opening. Gladiolus can also be attacked by the lily beetle, an insect that creates holes in the leaves and flower buds.

When stored, the bulbs are susceptible to rotting. It is crucial to pay attention to humidity and store them in suitable conditions. When they are in the ground, the issue remains the same; vigilance is required to avoid excess moisture and bulb rot.

Multiplication of gladioli: division and sowing

Gladiolus is primarily multiplied by separating the corms. It is also possible to sow it, but division remains the simplest and fastest technique!

Dividing Gladiolus

Gladiolus bulbs produce bulbils (or bulblets) around the main bulb. These are small white spheres attached to the base of the bulb. You can easily separate them from the original bulb to obtain new young plants. It is best to do this in autumn (once the foliage has dried), around early November, while you are digging up the bulbs to store them in frost-free conditions for winter.

1. Dig up the gladiolus bulbs in autumn.
2. Detach the bulblets located around the original bulb. Choose the largest ones.
3. Store them for winter in a box filled with sand.
4. Replant them the following spring, in April-May.

The bulblets will take two to three years before they start to flower.

Sowing Gladiolus Seeds

Sowing gladiolus is a bit tricky to succeed… It is easier and quicker to separate the corms! Nevertheless, if you wish to multiply it by sowing, do so preferably in early spring.

1. Take a pot and fill it with fine, sieved potting soil. Lightly firm it down and moisten the substrate.
2. Sow the seeds by spreading them over the surface.
3. Cover them with 1 to 2 centimetres of potting soil.
4. Water gently.

Place the pot at a temperature of around 15 °C in a bright location. Keep the substrate slightly moist until germination. It will take several years for the gladiolus to start flowering.

Associating Gladioli in the Garden

Gladiolus integrates easily into a flower bed or a colourful mixed border! Place it towards the back, behind shorter plants. Pair it with other full sun plants that flower in summer: dahlias, crocosmias, rudbeckias, nasturtiums… Gladiolus pairs perfectly with other impressive blooms, large, colourful, majestic flowers like those of Lilies or Dahlias… Moreover, you will create an ideal flower bed for composing bouquets!

A combination of gladiolus, dahlias, and lilies (photo Steven Bemelman – iBulb) / Dahlia, gladiolus, and pennisetum combination (photo Maayke de Ridder – iBulb) / Lily / Gladiolus ‘Princess Margaret Rose’ / Dahlia ‘Inflammation’ (photo F.D. Richards)

As they come in a very wide range of colours, with endless shades, gladiolus are perfect for creating stunning contrast effects, or conversely, harmonies with other flowers in the same tones! They are easy to pair with dahlias, as they also offer a wide colour palette… You will have no trouble finding them in shades that match perfectly!

Because they have a rigid and very upright habit, we recommend planting gladiolus alongside much softer, airy, and wispy plants: grasses, cosmos, sanguisorbas, gaura, Verbena bonariensis… They will bring a touch of lightness and softness! You can also scatter a few gladiolus in a flower bed, among shorter plants: their long flower spikes will add verticality, dynamism, and structure.

A combination of Gladiolus callianthus, agastache, phlox, Buenos Aires verbena, pennisetum (photo Maayke de Ridder – iBulb) / Pennisetum setaceum / Gladiolus callianthus (acidanthera) / Phlox ‘Lilac Time’ (photo Uleli)

Although gladiolus often have a reputation for being rigid plants with large, exuberant flowers, some are much more delicate and natural, allowing them to fit into a naturalistic or country garden composition. Opt for botanical gladiolus: Gladiolus byzantinus, Gladiolus callianthus, Gladiolus illyricus… You can plant them alongside some clumps of pennisetum and stipa, as well as Buenos Aires verbena, Gaura lindheimeri, or agastache.

For more inspiration, read: Gladiolus: 5 ideas for successful combinations