Invasive Plant of the Month: Yellow Iris (Iris pseudacorus)

You may be just one person, with one yard and one garden, but if you can eliminate the invasive plant species in your yard, you’ve taken a giant step to help the ecosystem.

If you can educate your neighbours about the dangers of invasive plants, you’ve taken an even greater step to help wildlife, the environment and the planet.

Invasive plants have little or no value for insects, birds or other wildlife. In fact, they cause harm, and invasive plants cause harm to our economy and human health as well.

Let’s educate people, just as we did with smoking and seatbelts.

Be patient with yourself and others, take your time, focus on getting rid of one or two invasives and then replant with non-invasive plants, or replant with natives to restore the health of the ecosystem, and bring back pollinators and other wildlife.

Yellow Iris is a perennial aquatic plant native to Europe, western Asia and North Africa. It was first introduced to North America in the 1800s as an ornamental plant for ponds and water gardens.

The plan has since spread to many waterways, including those in parts of southern Ontario.

Yellow Iris can grow in both treed and open wetlands, along river and lake edges, and on floodplains.

The plant spreads by seeds and by underground stems known as rhizomes that send out new shoots above the ground and roots below.

These rhizomes can develop into thick mats, consisting of several hundred plants.

Fragments of rhizomes that break off can also form new plants.

Impacts of Yellow Iris:

The dense stands of very thick mats of rhizomes and dead leaves can displace native plants and change wetlands to much drier environments.

The drier environment reduces habitat available for wildlife, including native fish habitat and bird nesting and rearing sites.

The dense mats can also block water flow in irrigation and flood control ditches.

Yellow Iris is poisonous to both humans and animals if eaten, and its sap can cause dermatitis.

How to Manage Yellow Iris:

Start with prevention.

Yellow Iris is still sold in nurseries. Do not buy or share this plant. Managing Yellow Iris is challenging but achievable with persistence and a multi-step approach.

Manual Removal:

Efforts are most likely to succeed when patches are small.

Start by removing all flowers and seed heads to deplete the seed bank. Dig up and remove plants including rhizomes to control spread.

Continue to monitor for re-growth as this process may take several years.

Caution – all plant parts can cause skin irritation. Ensure gloves, safety glasses and long-sleeved clothing is worn during any work with this plant.

Do not put plant material in the compost or municipal green waste.

Smothering:

Smothering or tarping is affecting for populations growing on land of water.

Start by cutting or mowing plants back, then cover with heavy PVC pond liner. Make sure you extend liner or at least one metre beyond the infestation and secure it.

Monitor regularly for re-growth, remove the barrier when rhizomes have turned dark brown and mushy.

Pond liner will likely need to be in place four to six months for success. Place all plant material in garbage for disposal.

Herbicide Treatment:

There is currently no chemical control available in Canada for Yellow Iris.

After removal, replant the area with regionally appropriate native plants. This step is essential to prevent reinfestation and to restore ecosystem health.

Native plants will also attract pollinators and wildlife, improving biodiversity in your garden.

A good alternative choice would be Cardinal Flower (Lobelia cardinalis).

Education is key to combating invasive plants. Learn to identify invasive plants and choose native or non-invasive alternatives for your garden.

Focus on managing one or two invasive plants at a time and be patient.

For more information visit www.ontarioinvasiveplants.ca or www.ontarioinvasiveplants.ca/resources/best-management-practices

Renee Sandelowsky and Helen Varekamp are volunteers for Canadian Coalition for Invasive Plant Regulation