CRD weed of the week the Yellow Flag Iris

Gardeners should be aware that the Yellow Flag Iris, while a beautiful exotic aquatic water plant, is a serious invasive species.

Gardeners should be aware that the Yellow Flag Iris, while a beautiful exotic aquatic water plant,  is a serious invasive species, reports the Cariboo Regional District.

This plant is native to Europe, the British Isles, North Africa and the Mediterranean region.

And as of right now, it is still being sold in nurseries and can be bought on the Internet, around the world.

Yellow Flag Iris grows about four feet tall with a robust stalk and the stems/leaves are long, dark green, flattened and sword like.

The leaves have a distinctive ridge in the mid-vein and they contain a sap that is toxic if ingested or can cause skin irritations.

The flowers are a vibrant yellow with three petals that are backwards curving. What makes this plant multiply so quickly, is that it spreads vegetatively and by seed.

If a piece of the roots breaks off, the piece is able to float down stream and re-sprout a new plant.

The seed pods of yellow flag can remain buoyant in the water for up to seven months.

Yellow Flag Iris can grow in a variety of different habitats including dry, high acidy or anoxia soils, brackish waters and in fresh or salt water.

It can be found in temperate wetland, along margins of lakes, ponds, ditches and slow moving rivers.

This invasive species is a major problem for aquatic habitat because of its ability to colonize so quickly and the roots form dense mats that are up to 30cm deep which choke-out much of the native vegetation.

Since it can form dense stands, it can change the width of water courses by compacting soil trapping sediments and increasing elevation.

It also affects the water flow of irrigation canals and flood control ditches.

There are Yellow Flag Iris infestations in Williams Lake that are currently being treated and recently the CRD Invasive Plant crews have inventoried new infestations along the shoreline of Lac La Hache.

Treatment options for Yellow Flag Iris are:

• Hand pulling by digging up the whole plant making sure you dig up the entire root and any fragments.

• Cutting the plants right to ground level, this will have to be done several times but can be affective.

All plant material must be bagged and disposed of in designated areas, such as invasive plant bins at your local landfill.

Do not compost invasive plants.

To stop the spread of Yellow Flag Iris:

1.) Learn to identify this aquatic exotic.

2.) Do not purchase and plant Yellow Flag Iris.

3.) Wash boats and other water recreation vehicles before leaving a lake.

4.) Minimize soil disturbance.

5.) Report any sightings to the CRD at 1-800-665-1636, online at or email

Instead of planting Yellow Flag Iris in your garden try these alternatives: Japanese Iris (Iris nsata), Siberian Iris (Iris Sibirica) or Laevigata Iris (Iris laevigata).


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