Dwarf iris

Dwarf iris: how do you recognise it?

Habit

Low tufts 10–15 cm tall that spread by rhizomes into a mat about 30 cm wide.

Leaves

Narrow, grey-green sword-shaped leaves in small fans.

Flower

A bearded iris in miniature: three upright and three drooping petals, the drooping ones with a hairy beard, on a very short stem, in April–May.

Colour

Purple, blue, yellow, white, cream or two-tone; in the wild, several colours often grow together in one population.

Roots

A shallow, creeping rhizome that sits right at the soil surface.

Flowering: April–May · Plants: July–September · Pruning: June and November

Why grow it?

• One of the earliest irises: bright flowers as early as April.
• Small and compact: perfect for a rock garden, a gravel bed, the edge of a border or a trough.
• Drought tolerant and lime-loving: suits the sunniest, driest spots.
• The grey-green leaf fans give structure even after flowering.
• Slowly spreads into a dense little mat that bears more flowers every year.

Dwarf iris: where does it grow best?

• Full sun: the rhizome needs to bake in summer to flower the following year.
• Free-draining, chalky to neutral soil: sand or loam, possibly with grit. No acid or wet soil.
• Dry: a rock garden, a bank, the top of a low wall or a trough.
• Plant 15–20 cm apart, at the front and out of the shade of taller plants.

Light

Sun

Soil type

Sand or loam

Acidity

Neutral or chalky

Moisture

Dry

Size

0.15 m tall, 0.3 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Aubrieta: Low cushions that flower at the same time, on a sunny wall or in a rock garden.
• Pasque flower: Silky flowers and feathery seed heads in the same spring, also on chalk.
• Houseleek: Also drought tolerant, for a trough or rock garden.
• Thyme: Fragrant mats that flower after the iris.
• Species tulip: Small tulips that flower at the same time, in the same sunny spot.

Dwarf iris: when and how to plant it?

Plant in July–September.

1. Plant from July to September, after flowering, so the rhizome can establish before winter.
2. On heavier soil, work in some grit or coarse sand; no fresh manure.
3. Lay the rhizome flat and shallow: the top sits at the soil surface and the roots are spread out in the soil.
4. Firm the soil well around the roots, but do not cover the rhizome itself.
5. Leave 15–20 cm between plants.
6. Water in well once after planting, then only during prolonged drought; do not mulch over the rhizome.

Care

Water

Hardly ever once established; too much water makes the rhizome rot.

Feeding

Little needed: a little low-nitrogen organic fertiliser in March. No fresh manure or thick layer of compost.

Keep rhizome clear

Keep the rhizome free of mulch, fallen leaves and weeds, so it gets sun and stays dry.

Spent flowers

Cut off faded flowers and their little stems; it looks tidier.

Leaves

Do not cut the green leaves short in summer: the plant needs them to build up strength for the next flowering.

Dividing

Every 3–4 years, when the centre of the mat goes bare and flowers less.

Tip: Plant the rhizome so shallowly that the top is just visible and never cover it: it needs to bake in summer to flower freely the following spring.

Dwarf iris: when to prune it?

Pruning months: June and November.

When: It hardly needs pruning. After flowering, in June, cut off the spent flowers, and in November the dead leaves.

How:

• Cut spent flowers and their stems off just above the leaf fan.
• Leave the green leaves until they turn yellow or brown by themselves.
• In November, remove brown and dead leaves so the rhizome does not rot and slugs have fewer hiding places.

Caution: Wear gloves when dividing or cleaning the rhizomes: the sap can irritate the skin.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

After flowering, from July to September: lift the mat, break or cut the rhizome into pieces that each have a leaf fan and healthy roots, and replant them shallowly. Discard old pieces without leaves.

Seed

Possible for the species: sow ripe seed in autumn in a pot left outdoors. Germination is slow and seedlings only flower after a few years; cultivars do not come true from seed.

Dwarf iris: how does it get through the winter?

Hardy to −35 °C.

• Very hardy, to about −35 °C: cold is no problem.
• Wet winters are the biggest danger: in wet soil the rhizome rots.
• Do not cover it with leaves or mulch; a layer of gravel around the base keeps the rhizome dry.
• In a trough or pot: make sure drainage is good and move it under a roof overhang during prolonged rain if needed.

Diseases and pests

• Rhizome rot: The rhizome turns soft and smelly and the leaves fall over. Cut away the rotten part back to healthy tissue, let the wound dry in the sun and replant in a drier spot.
• Few flowers: Too much shade, planted too deep or an overcrowded mat. Give it more sun, plant shallower or divide it.
• Leaf spot: Small brown spots with a yellow edge on the leaves, especially in wet years. Cut off affected leaves and clear away dead ones.
• Slugs: They eat flower buds and young leaves in spring. Pick them off in the evening and keep the spot free of fallen leaves.

Through the year

• March: Clear fallen leaves off the rhizomes. Give a little low-nitrogen fertiliser if needed.
• April: Flowering begins. Watch for slugs.
• May: In flower. Remove spent flowers.
• June: Cut off the last spent stems. Leave the leaves.
• July: Plant and divide.
• August: Plant and divide. Let the rhizomes bake in the sun.
• September: Last month for planting. Sow ripe seed.
• November: Remove dead leaves. Do not cover.

Edible and useful

Not edible. All parts of these irises are poisonous, especially the rhizome: eating any causes vomiting, stomach ache and diarrhoea, and dogs, cats and grazing livestock fall ill from it too. The main risk comes when you divide the clumps: clear up the loose pieces of rhizome straight away, do not leave them lying where children play or dogs dig, and do not throw them into a field or run. Siberian and Japanese iris like the edge of a pond, where without flowers their leaves look like those of other waterside plants: do not eat anything from a waterside plant you are not sure of. The sap can irritate the skin: wear gloves when dividing and cutting back. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• Pumila means ‘dwarf’ or ‘small’ in Latin.
• In wild populations, purple, yellow and white plants often grow side by side: the species is very variable in colour.
• Crossing the dwarf iris with tall bearded irises produced the standard dwarf bearded irises seen in many gardens today.