Iris ensata - Japanese Iris, Bog Plant

Iris ensata (also sold as Iris kaempferi), known as Japanese iris, forms dense clumps of sword-shaped leaves with a prominent midrib. In June and July it carries large, rich violet-purple flowers, 10–12 cm across, with a small white or yellow flash on the broad falls. It flowers later than Iris laevigata.

Japanese iris at a glance

Botanical name	Iris ensata (syn. I. kaempferi)
Common name	Japanese iris, Japanese flag
Plant type	Clump-forming iris; dies back in winter
Height and spread	About 80 cm tall (up to 1 m), up to 50 cm wide
Flowers	Rich violet-purple, 10–12 cm across, with a white or yellow flash, June and July
Position	Full sun or part shade
Soil	Moist to wet, deep, humus-rich, acid soil; avoid lime
Pond depth	None in winter – bog garden or damp soil
Hardiness	RHS H6 – hardy in a very cold winter (-20 to -15°C)
Native to	East Asia (not UK native)

Can Iris ensata grow in a pond?

Not all year. It likes plenty of water in summer, but its crowns rot in standing water over winter. Grow it in a bog garden or damp soil at the pond edge. If you stand pots in shallow water in summer, raise them so the crown is above the water from autumn to spring.

What soil does it need?

Moist, rich, acid soil. It does not like lime, so use ericaceous compost in pots if your soil is chalky or alkaline.

How to plant and care for it

Plant in spring or summer. Remove dying leaves in autumn. Watch for slugs, snails and thrips.

Is it poisonous?

Yes. Irises are harmful if eaten by people or pets, so wear gloves when handling it.

Which size should I buy?

Bare-root plants (7 cm, 9 cm, 1 litre and 3 litre) arrive without a pot or compost and are the most economical way to plant a group. Potted plants (9 cm, 1 litre and 3 litre) arrive growing in our peat-free compost and give a faster display. Packs of 3 come in 7 cm, 9 cm, 1 litre and 3 litre bare-root sizes and cost less per plant. The 2x Pot & Compost option is two plants supplied with pots and compost.