How to Grow Gladioli in the UK

Gladioli are some of the most eye-catching summer flowers you can grow. Their tall spikes reach 60-150cm and come in almost every colour, from deep velvety reds and purples to soft pinks, whites and bright yellows. Each corm makes a new corm and a few tiny cormlets every year, so you get more plants for free.

Gladioli are part of the iris family and mostly come from South Africa. The name comes from the Latin for sword, after their flat, blade-like leaves. The RHS gladiolus growing guide is a handy extra reference. Here’s how to grow them, from choosing a type to storing the corms over winter.

Planting gladioli corms in spring, pointy end up, 10-15cm deep.

What types of gladioli can I grow in the UK?

There are five main groups of gladioli, each suited to different spots. Knowing which is which saves disappointment.

Large-flowered gladioli (Grandiflorus)

The classic show gladioli and the most popular. Tall stems reach 90-150cm with big, ruffled flowers in every shade from white to almost black. ‘Peter Pears’ (salmon-orange) and ‘White Prosperity’ are reliable choices. They need staking and are superb as cut flowers.

Nanus gladioli

Compact plants just 40-60cm tall, with smaller, daintier flowers. They’re a bit tougher than other groups and sometimes survive outdoors in sheltered, well-drained southern gardens, but it’s still safest to lift them. ‘Nymph’ (white with pink marks) and ‘Impressive’ (pink) are easy to find. Plant in groups of 10-15 for the best effect.

Primulinus gladioli

Mid-height plants, 60-90cm, with elegant hooded top petals. They look more natural than the big show types, with fewer flowers per spike and a relaxed, graceful look. Lovely in cottage borders. Often found in warm yellows, oranges and salmons.

Butterfly gladioli

A similar height, 60-90cm, but with dramatic markings and contrasting blotches in the throat of each flower. Their bold colours make them striking in a vase.

Hardy Gladiolus communis subsp. byzantinus

The one hardy gladiolus for UK gardens. It has magenta-pink flowers on 60-90cm stems in June, earlier than the others, and spreads happily in well-drained soil by corms and seed. Plant it and forget it. It looks great with dahlias and other summer flowers. For scented spikes from another South African corm grown the same way, try Acidanthera, the fragrant Abyssinian gladiolus.

Byzantinus is the one gladiolus you can plant and leave in the ground. It flowers in June and spreads happily in soil that drains well.

Gladioli type comparison

How to buy good quality gladioli corms

Choose firm, plump corms with no mould, soft spots or deep marks. Bigger corms give stronger spikes in the first year. Avoid any that feel light or papery, as they’ve dried out and may not grow.

Buy from a good bulb supplier rather than the bargain bin. Order in January or February for the widest choice. Most suppliers send corms out from February to April.

Have a look under the papery skin for tiny black or brown insects before planting. These are thrips. Throw away any badly affected corms.

Pick firm, plump corms with no soft spots or mould. Light, papery ones have dried out and may not grow.

When and how to plant gladioli in the UK

Timing

Plant outdoors from mid-April in southern England and early May further north. The soil needs to have warmed up. In a cold, wet spring, wait a week or two rather than planting into cold, soggy soil where the corms may rot.

For the earliest flowers, start corms in 9cm pots of multipurpose compost under cover from mid-March. A frost-free greenhouse, conservatory or bright windowsill all work. Harden them off and plant out after the last frost.

Planting depth and spacing

Plant corms 10-15cm deep, pointy end up. Space them 10-15cm apart for a packed display, or 20cm apart for bigger spikes. Planting at the full 15cm holds tall stems steadier, so you need less staking.

On heavy clay, put a little grit under each corm to help drainage and stop rot. On sandy soil, add some compost to hold moisture. Gladioli are hungry and like rich, well-drained soil in full sun, with at least six hours of sun a day.

Planting in rows vs groups

For cutting, plant in straight rows 30cm apart, which makes picking, staking and weeding easier. For borders, plant in loose groups of 7-15. Odd numbers look more natural. Tuck groups between plants such as lilies and late-summer asters.

How to do succession planting for continuous gladioli

Plant a fresh batch of corms every two weeks from mid-April to early June. It turns a short burst of flowers into months of colour from late July into October.

A simple plan for the Midlands:

• Batch 1: Mid-April (flowers late July)
• Batch 2: Early May (flowers mid-August)
• Batch 3: Mid-May (flowers late August)
• Batch 4: Early June (flowers mid-September)
• Batch 5: Mid-June (flowers early October, weather permitting)

Each batch takes roughly three months from planting to flowering, a little longer for the big show types. A cool or warm summer shifts things a bit.

It also spreads out the lifting in autumn, as the early batches finish first. It’s worth fitting into your flower planting calendar for the year.

How to stake and support gladioli

Stake tall varieties when the stems are about 15-20cm tall. Big show types get top-heavy once the spike forms and snap easily in the wind.

Three easy ways to support them:

1. Single canes: Push a 120cm cane in next to each corm at planting. Tie the stem loosely with soft string as it grows, every 20-30cm. Best for a few plants.

2. Grow-through supports: Put metal ring supports or pea netting over the planting before the shoots come up. The stems grow up through the grid. Best for groups.

3. String lines: For rows of cut flowers, hammer a post in at each end and run strings along at 30cm intervals.

The shorter nanus, primulinus and butterfly types rarely need staking unless your garden is very windy. Hardy byzantinus holds itself up well in a mixed border.

Gladioli are lovely, long-lasting cut flowers.

How to grow gladioli as cut flowers

Cut gladioli when the bottom two or three flowers have opened. The rest of the buds keep opening in the vase over the next week or so, making them one of the longest-lasting summer cut flowers. Our guide to conditioning cut flowers shows how to make all your flowers last longer.

Cutting technique

Use a sharp, clean knife or secateurs. Cut at an angle early in the morning while it’s cool. Leave at least four leaves on the plant, as they feed the new corm forming underground. Take too many and next year’s corm will be weaker.

Cut when the bottom two or three flowers have opened, and leave at least four leaves behind to feed next year’s corm.

Vase care

Strip off any leaves that would sit in the water. Stand the stems in deep, clean water with flower food, and change the water every two days. Pinch off the lowest flowers as they fade so the top buds open. Keep the vase out of direct sun and away from the fruit bowl, as ripening fruit makes flowers fade faster.

Best varieties for cutting

The big show types give the most dramatic vases. ‘White Prosperity’, ‘Peter Pears’ (salmon), ‘Plum Tart’ (deep plum) and ‘Green Star’ (lime green) are all lovely. For smaller, relaxed arrangements, try nanus types like ‘Nymph’. Grow them with other types of flowers for mixed bunches all summer. For scent to go with the colour, add a row of tuberose, the most heavily scented summer bulb.

How to feed and water gladioli

Feed every two weeks with tomato feed once the flower spike starts to show. It gives strong spikes and helps the new corm grow for next year.

Water well in dry spells, especially once the spike is forming. Gladioli have shallow roots and suffer quickly in drought. A deep weekly soak is better than a little every day. Mulch around them with compost or bark to keep the soil moist and the weeds down.

Stop feeding once flowering is over, so the plant can put its energy into the new corm.

How to deal with gladiolus thrips

Gladiolus thrips are the main gladioli pest in the UK. These tiny insects rasp at leaves and flowers, leaving silvery streaks on the leaves and white flecks on the petals. Badly affected plants have twisted, discoloured flowers that may not open properly.

Identifying thrips damage

Look for tiny black or brown insects under the leaves and on the flower buds. Damage gets worse in hot, dry summers, when they breed quickly.

Silvery streaks on the leaves and flecked, twisted flowers point to thrips. They’re worst in hot, dry summers, so keep plants well watered.

Treatment

• Encourage helpers: Ladybirds and lacewings eat thrips, so a wildlife-friendly garden helps.
• Good habits: Remove and bin badly affected leaves rather than composting them. Keep plants well watered in hot weather.
• Prevention: Plant gladioli in a different spot each year. Check stored corms over winter and throw out any with thrips.
• If you need a spray: Use an approved insecticide exactly as the label says, and avoid spraying open flowers that bees visit.

Other gladioli pests and diseases

Grey mould (Botrytis)

Brown patches on leaves and fuzzy grey mould on flowers, worse in wet summers and crowded planting. Space corms properly, remove affected leaves and water at the base.

Fusarium wilt (Gladiolus yellows)

A soil-borne disease that makes leaves yellow and wilt from the bottom up. The corms get dark, sunken patches. There’s no cure. Dig up and bin affected plants and corms, and don’t grow gladioli in that soil again for several years.

Slugs and snails

Young shoots are at risk in spring. Use wildlife-friendly ferric phosphate pellets or beer traps, and check plants at dusk in damp weather.

Corm rot

Soft, mushy corms with a sour smell. Usually caused by waterlogged soil or storing corms damp. Improve drainage at planting and make sure corms are bone-dry before you store them.

Lift gladioli corms about six weeks after flowering, before the first hard frost.

How to lift and store gladioli corms for winter

Lift the corms about six weeks after flowering, before the first hard frost. In most of the UK that’s September for early batches and October or November for later ones. Don’t rush, as the new corm needs those weeks to fill out.

Step-by-step lifting process

1. Cut back the leaves to about 5cm once they start to yellow.
2. Lift gently with a fork, pushing it in well away from the plant so you don’t spear the corms.
3. Shake off the loose soil. You’ll see the new corm sitting on top of the old, shrivelled one.
4. Snap off the old corm from the bottom. It comes away easily.
5. Pick off the cormlets, the tiny pea-sized corms around the base. Keep them to grow on, or throw them away.
6. Dry the corms somewhere warm and airy, like a greenhouse, shed or garage, for 2-3 weeks, spread out on newspaper or trays.
7. Clean them once dry by removing loose skins and old roots.

Winter storage

Store the dry corms in paper bags, net bags or trays somewhere cool, dry and frost-free, around 5-10C. A cold spare room, frost-free garage or cool shed is fine. Avoid airtight boxes, which trap moisture and cause rot. Check them every month and throw out any that go soft or mouldy.

Cormlets can be grown on to flowering size in two or three years. Store them the same way and plant them 5cm deep in spring. They make leaves in year one but usually don’t flower until year two or three.

Can I overwinter gladioli in the ground?

Only Gladiolus communis subsp. byzantinus reliably survives UK winters in the ground. It’s hardy and spreads happily in well-drained soil across much of the country, with magenta-pink flowers in June.

All the others can be killed by frost and winter wet. In very mild, well-drained coastal gardens in the far south-west, the big show types sometimes survive under a thick mulch of bark or straw. It’s a gamble, though. In most of the UK, it’s safest to lift and store them every autumn.

Nanus types are a little tougher and sometimes survive in sheltered town gardens with good drainage. If you want to try, plant them 15cm deep and mulch thickly with bracken or straw in November. Be ready to lose a few in a hard winter.

Growing gladioli in containers

Gladioli grow well in pots at least 30cm deep and 20cm across. Five to seven corms per pot gives a full display. Use multipurpose compost with some perlite mixed in for drainage.

Plant 10cm deep. Water when the top few centimetres of compost dry out. Feed every two weeks with tomato feed once the spikes appear. Support each stem with a slim cane. When the leaves die back, lift the corms or move the pot somewhere frost-free.

The shorter nanus and butterfly types look best in pots, as they don’t get top-heavy. Stand them on a sunny patio.

Month-by-month gladioli growing calendar

Frequently asked questions

When should I plant gladioli corms in the UK?

Plant them outdoors from mid-April to late May. Mid-April is usually fine in southern England, but wait until late April or May further north. For earlier flowers, start corms in pots under cover in March and plant them out after the last frost. Plant a batch every couple of weeks for a longer show.

How deep should I plant gladioli corms?

Plant them 10-15cm deep and 10-15cm apart, pointy end up. Deeper planting holds the tall stems steadier, so you need less staking. In light, sandy soil, go the full 15cm. In heavy soil, about 10cm is enough, with some grit underneath for drainage.

Do I need to lift gladioli corms in winter?

Yes, most gladioli need lifting, as they aren’t reliably hardy. Gladiolus communis subsp. byzantinus is the main exception and can stay in the ground in most of the UK. Lift the others once the leaves start to yellow in autumn. Dry the corms for a few weeks, then store them somewhere cool, dry and frost-free.

Why are my gladioli leaves turning silvery?

Silvery streaks are usually caused by gladiolus thrips. These tiny insects feed on leaves and flowers, leaving pale, silvery marks. Badly affected plants have twisted, discoloured flowers. Remove badly affected leaves and keep plants well watered. Check stored corms and throw out damaged ones. If needed, use an approved insecticide as the label directs.

Can I grow gladioli in pots?

Yes, they grow well in pots at least 30cm deep. Plant several corms about 10cm deep in multipurpose compost with some grit or perlite. Support the stems with canes as they grow. Water regularly and feed every two weeks with tomato feed once the flower spikes appear.

How long do gladioli last in a vase?

They usually last about a week, sometimes longer. Cut the stems when the bottom two or three flowers have opened, with a sharp slanting cut. Pinch off the lowest flowers as they fade so the upper buds can open. Change the water every couple of days, add flower food and keep the vase out of sun and away from fruit.

Are gladioli hardy in the UK?

Most gladioli aren’t hardy and won’t reliably survive winter outside. The exception is Gladiolus communis subsp. byzantinus, which is hardy and spreads happily in many UK gardens. Lift the large-flowered, butterfly, primulinus and nanus types in autumn and store them frost-free. In very mild areas with sharp drainage, some may survive under a thick mulch.