Iris tuberosa

RHS Plant Profile

snake's head iris

Other common names

black widow, onion iris, widow iris

Synonyms

Iris hermodactylus tuberosus
Hermodactylus tuberosus

Alpine Rockery Herbaceous Perennial

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A tuberous perennial with lance-shaped, glaucous green leaves which appear in winter or early spring. Flowers are borne rather lower than leaf tips, on stems to 40cm, and are a striking combination of greenish-yellow standards with purplish-brown to blackish falls

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

0.1-0.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.1-0.5 metres
Max Height: 0.1-0.5 metres

Growing Conditions

Chalk Loam Sand

Moisture: Well–drained
pH: Alkaline or Neutral

Position

Full sun

Aspect: South–facing
Exposure: Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

H1A: under glass all year (>15C)
H1B: can be grown outside in the summer (10 - 15)
H1C: can be grown outside in the summer (5 - 10)
H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
H4: hardy through most of the UK (-10 to -5)
H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
H6: hardy in all of UK and northern Europe (-20 to -15)
H7: hardy in the severest European continental climates (< -20): H5

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Iridaceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Bushy
Potentially harmful: Harmful if eaten. Wear gloves and other protective equipment when handling. Pets: Harmful if eaten. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus: Iris may be rhizomatous or bulbous perennials, with narrow leaves and erect stems bearing flowers with 3 large spreading or pendent fall petals, alternating with 3 erect, often smaller, standard petals, in late winter, spring or early summer
Name Status: Correct
Plant Range: S Europe

How to Grow

Cultivation

Plant tubers 10cm (4in) deep in autumn, in moderately fertile, sharply drained alkaline soil in full sun. Dry summers encourage flowering

Propagation

Propagate by division as soon as the leaves have died back in early summer

Suggested planting locations and garden types

Rock garden
Wildflower meadow
Cottage and informal garden
Mediterranean climate plants
Low Maintenance
Flower borders and beds
Banks and slopes
Cut flowers

Pruning

No pruning required

Pests

May be susceptible to slugs, snails and thrips

Diseases

May be susceptible to aphid-borne viruses, bacterial soft rot and grey moulds; see Iris diseases