English iris

English iris: how do you recognise it?

Habit

Upright bulbous plant about 50 cm tall and 10 cm wide, forming an airy clump in a group.

Leaves

Broad, sword-shaped, grey-green with a clear midrib; they die back after flowering.

Flower

Large flowers with drooping outer petals and upright inner petals, from June to July; each flower is short-lived, but several buds open in succession.

Colour

Blue-purple to violet, with a yellow blotch on the drooping petals; white and pale blue also occur.

Bulb

Oval bulb with a brown, papery coat; it forms new bulblets every year.

Flowering: June–July · Plants: September–October

Why grow it?

• Flowers in June–July, when the spring bulbous irises are long over.
• Deep blue to purple flowers that combine well with pink and white in the border.
• One of the few bulbous irises that also grows well in moist, heavier soil.
• Bees visit the flowers, and they make lovely cut flowers.
• Fully hardy (down to about −20 °C) and can stay in the ground for many years.

English iris: where does it grow best?

• Sun to partial shade; it flowers best in sun, as long as the soil does not dry out in summer.
• Rich, moisture-retentive soil: loam or clay, preferably with a little compost; acid, neutral or chalky are all fine.
• Keep the soil evenly moist in summer, but make sure water can drain away in winter: standing water makes the bulb rot.
• Sheltered from strong wind; the stems are slender and can blow over.
• Plant the bulbs 10–15 cm apart, in small groups among perennials.

Light

Sun and partial shade

Soil type

Loam or clay

Acidity

Not fussy

Moisture

Normal or wet

Size

0.5 m tall, 0.1 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Cranesbill: Flowers at the same time; blue and pink side by side.
• Lady’s mantle: Frothy yellow flowers and leaves fill the lower part of the border.
• Daylily: Takes over when the irises have finished.
• Roses: The iris flowers stand out well between low shrub roses.

English iris: when and how to plant it?

Plant in September–October.

1. Plant in September–October, as soon as you have the bulbs; they should not lie in the bag for long.
2. Dig a hole about 10 cm deep and mix heavy clay with compost and some coarse sand.
3. Set the bulbs pointed end up, 10–15 cm apart.
4. Cover with soil and water at once, even if the autumn is dry.
5. Spread a layer of about 5 cm of leaf mould or fine mulch over the bulbs against frost and drying out.

Care

Water

Keep the soil evenly moist during the growing season, especially from May to July. In a dry spell, water generously at the base.

Feeding

In spring, a little compost or bulb fertiliser. Not too much nitrogen: it gives soft leaves.

Mulching

A layer of compost or leaf mould keeps the soil cool and moist in summer.

Spent flowers

Cut spent flowers off to prevent seed forming; the bulb stays stronger.

Dividing

Divide crowded clumps every 3–4 years, when flowering declines.

Tip: Unlike other bulbous irises, it wants soil that does not dry out in summer. Plant it in groups among perennials: their leaves keep the soil around the bulb moist and cool.

English iris: when to prune it?

When: Pruning is not needed. Cut off spent flowers in July and remove the leaves only when they are completely yellow and withered, in August–September.

How:

• Cut the spent flower stem off just above the ground.
• Leave the leaves until they turn yellow; they feed the bulb for next year.
• Remove the withered leaves in autumn with sharp scissors.

Caution: Do not cut the green leaves too early: the bulb would flower less next year.

Pruning calendar and basic rules

Propagation

Division

In August–September, when the leaves are yellow: lift the clump, separate the bulbs and replant them at once at 10 cm deep.

Seed

Sow in autumn in pots outdoors; seedlings take several years to flower. Division is much faster.

English iris: how does it get through the winter?

Hardy to −20 °C.

• Fully hardy in Belgium (down to about −20 °C): no protection needed if the soil is free-draining.
• A layer of 5–10 cm of compost or dry leaves over the bulbs protects against hard frost and drying out.
• In a pot: place the pot in a sheltered spot against a wall and do not let it stand in water.

Diseases and pests

• Slugs: They eat young leaves and buds in spring. Pick them off by hand in the evening and do not leave damp boards in the border.
• Bulb rot: If the soil is too wet in winter, the bulbs rot. Plant in free-draining soil and mix clay with sand.
• Leaf spot: Brown spots on the leaves in damp weather. Cut off affected leaves, leave space between plants and do not water over the foliage.
• Aphids: They sit on young shoots and can spread virus. Rinse them off with water or let ladybirds do their work.

Through the year

• March: Young shoots appear. Watch for slugs.
• April: Leaves grow. Apply compost or bulb fertiliser.
• May: Buds form. Water in dry spells.
• June: Flowering begins. Cut flowers for the vase.
• July: Flowering. Cut off spent stems.
• August: Leaves turn yellow. Lift and divide clumps if needed.
• September: Plant or replant.
• October: Plant. Mulch with compost.
• November: Last chance to plant.
• December: Resting underground.

Edible and useful

Not edible. All parts of these bulbous irises are poisonous, especially the bulb: eating any causes vomiting, stomach ache and diarrhoea, and dogs and cats fall ill from it too. In autumn the small bulbs look like shallots or onion sets: do not store them with the kitchen onions, plant them straight away and clear up empty bags and loose bulbs. Dogs that dig easily bring them up, and dwarf irises in a pot indoors are often at a child’s height. People who cut a lot of flowers or plant a lot of bulbs sometimes get red, itchy skin from the sap: wear gloves and wash your hands afterwards. If an animal has eaten some, call your vet. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• It is called English iris, but it originally comes from the Pyrenees; in England it has been grown for centuries.
• It flowers in summer, after the Spanish and Dutch irises, and so extends the iris season.
• It belongs to the same group as the Spanish and Dutch irises: the so-called Xiphium irises.