Blue Flag / Poison Flag (Iris versicolor) – Showy Non-Native Flag Iris for Shallow Edges & Bog Gardens (Peat-Free, Pesticide-Free)

A handsome North American flag iris with bold violet-blue falls, gold signals and fine veining, Iris versicolor lights up the pond collar and very shallow shelf from early to mid-summer. Sword-like foliage forms upright fans that read clean and architectural, while clumps provide edge cover and emergence stems for aquatic insects. Expect around 60-90 cm in flower with a 30-60 cm spread; happiest in consistently moist to wet soil or with the crown set at water level to 0-5(-10) cm under water (it’s not a deep-water plant). Use as a mid/back accent behind low edge natives to build a layered, natural shoreline.

Where it thrives

• Light: Full sun to light/partial shade (best flowering in sun)

• Moisture/Zone: Pond collar / very shallow shelf; crown at water level or with 0-5(-10) cm water above the soil

• Setting: Naturalistic rims, basketed spots on the shelf, or damp borders that stay evenly moist; pairs well with Water Mint, sedges, Purple Loosestrife

Planting & care

• Plant rhizomes in a mesh aquatic basket with peat-free aquatic/bog compost; top with washed grit to prevent float

• Remove spent stems after flowering; cut back old leaves in late winter/early spring

• Lift and divide every 3-4 years (warm months) to refresh clumps and manage footprint

• Use rainwater where possible in hard-water areas for cleaner growth

Safety (important & honest):
All irises can irritate skin/eyes and are toxic if ingested (people, pets, livestock) – hence the common name “Poison Flag.” Wear gloves when dividing; do not ingest. Keep plant material and soil out of natural watercourses.

Truth-first wildlife note:
Flag irises offer moderate pollinator value – bees will use the open falls and signals – while the vertical fans deliver strong emergence structure and edge cover. Surround with single-flowered UK natives to provide a fuller nectar ladder through the season.

Joel says…
“Blue Flag gives you that crisp iris architecture with rich colour. Keep the crown at water level, basket it for control, and split it when the clump fattens.”

IMPORTANT NOTE: If you are ordering perennials between the months of October and March, including aquatic plants, please be aware that this is the dormant phase for perennials, so your plants may arrive showing potentially little or no top growth at this stage, or can in some cases still have some old leaves from last year showing also. Please don’t worry, as this is all quite normal. Once the weather warms up in spring, you will start to see fresh growth and activity! If you ever have any concerns at all, please just message the team on [email protected] and we’ll always do our best to help.