Yellow flag iris.

At a glance

Care level

Easy

Plant type

Herbaceous perennial

Light

Full sun to partial shade

Indoor light

bright-indirect

Water

Every 0 to 1 days

Mature size

3-5 feet tall, 2-4 feet wide

Growth rate

fast

Hardiness

USDA 3 to 9

Bloom time

Late spring to early summer

Care

Ensure it has consistently moist to wet soil, as it loves standing water. Remove spent flower stalks to encourage more blooms and prevent unwanted seeding. Be mindful of its vigorous spreading habit in garden settings.

Watering

Prefers to be waterlogged or have consistently wet soil; do not allow it to dry out.

Feeding

Generally not needed if grown in nutrient-rich soil or natural wetland conditions; a light feed in spring can be beneficial.

Pruning

Cut back dead foliage in late fall or early spring to tidy up the plant and remove potential overwintering pests.

Repotting

Divide clumps every 2-3 years when they become overcrowded to maintain vigor and control spread.

Soil

Clay, Loam, Sandy; consistently moist to wet

Soil pH

5.5-7.5

Temperature

-30 to 35°C

Humidity

60 to 100%

Safety

People

All parts of the plant contain toxins that can cause skin irritation and gastrointestinal upset if ingested.

Pets

This plant can be toxic if ingested by pets, causing gastrointestinal upset.

Children

The plant's toxicity means children should be prevented from ingesting any part of it.

Contact allergens

The sap can cause skin irritation in sensitive individuals.

Airborne allergens

Pollen may cause mild respiratory irritation for some people.

Edibility

This plant is not considered edible for humans.

How to identify it

• Erect, sword-shaped leaves
• Bright yellow, iris-like flowers
• Flowers have dark veins
• Grows in or near water
• Rhizomatous root system

Height

0.9 to 1.5m

Spread

0.6 to 1.2m

Leaves

Green, evergreen

Flowers

Yellow, 7 to 10cm

Fruit

Green, Brown, Late summer to fall

Common problems

• Iris borer — This pest bores into the rhizomes and leaves, causing damage and weakening the plant.
• Fungal leaf spot — Causes spots on the leaves, which can lead to reduced vigor.
• Invasive spread — Aggressively colonizes wetlands, outcompeting native species.

Growing it

Propagation

Division, Seed

When to plant

Spring, Fall

When planting yellow flag iris, ensure you are in an area where its invasive tendencies can be managed or are not a concern, such as a contained water garden.

Grows well with

• Cattail — These plants share similar wet habitat preferences and can create a cohesive wetland planting.
• Water Lily — Both thrive in water gardens and provide complementary foliage and floral interest.
• Pickerelweed — It enjoys wet conditions and offers vertical structure and flower spikes that complement the iris.

Keep away from

• Purple Loosestrife — Both are invasive in wetlands and compete fiercely for resources and space.
• Reed Canary Grass — This grass can form dense monocultures that outcompete and displace other wetland vegetation.

Similar species

• Siberian Iris — It has a similar iris form but prefers drier conditions and is not invasive.
• Blue Flag Iris — This native North American iris is also a wetland plant but is generally less aggressive and has blue-purple flowers.

Science

Family

Iridaceae

Genus

Iris

Order

Asparagales

Class

Liliopsida

Native range

Europe, North Africa, and Western Asia

Conservation

Yellow flag iris is considered an invasive species in many regions outside its native range.

It thrives in shallow water or saturated soils, forming dense stands that can alter wetland ecosystems.

Value to wildlife

nectar source, pollen source

Pollinators

bees, butterflies, moths

Uses

ornamental, wetland restoration (caution: invasive)

Taxonomy resolved against GBIF.

Questions people ask

What are the growing conditions for Iris pseudacorus?

It prefers full sun to partial shade and consistently moist to waterlogged soil.

How tall does it get?

It typically grows 2 to 4 feet tall.

When does it bloom?

It usually blooms in late spring to early summer.

Is it suitable for a water garden?

Yes, it's excellent for water gardens, pond edges, and marshy areas, but be mindful of its invasive potential.

Where the name comes from

The common name 'yellow flag iris' comes from its striking yellow flowers and flag-like leaves. The scientific name 'pseudacorus' means 'false acorus,' referring to its resemblance to the sweet flag plant (Acorus calamus).

Good to know

• It's a wetland plant that thrives in moist to wet conditions.
• The flowers are bright yellow and quite showy.
• It spreads rapidly via rhizomes and seeds.
• It's native to Europe, North Africa, and Western Asia.