Invasive Plant of the Month: English Ivy (Hedera helix)

Ontario has 441 known invasive plant species, the highest of all the provinces.

Invasive plants can reduce crop yield and increase the use of herbicides for farmers, increasing costs and reducing crop values.

Invasive plants can reduce forest regeneration by competing with tree seedlings.

In natural areas, invasive plants affect species diversity and health by reducing available resources.

Human health can be affected by invasive plant species such as toxic Giant Hogweed and Wild Parsnip.

Recreation areas overrun by invasive plants can be less enjoyable due to increased number of ticks, difficulty walking through a trail filled with dense growth, fewer birds and burs on clothing and pets.

Focus on English Ivy (Hedera helix):

English Ivy is native to Europe, western Asia and northern Africa. It was introduced to Canada in the 1800s as an ornamental plant.

It has been developed into hundreds of varieties and can now be found in gardens throughout North America.

Although technically a vine, this evergreen perennial is commonly used as a groundcover in dense shade.

Whether in shade or sun, English Ivy will persist and spread vegetatively through its long vines that root at the nodes in almost any soil type and will block sunlight from other plants.

It is easily identified by its dark green, three-lobed leaves, placed alternatively on its flexible woody vine.

Despite its pervasiveness in gardens and nearby natural areas, not a single North American animal uses English Ivy for food.

Indeed, this is one of the causes of its invasive nature, the other being its considerable adaptability.

More surprisingly, English Ivy is still readily for sale in garden centres.

The fruits are toxic to humans and livestock, and its sap can irritate skin.

Birds eat the berries and are responsible for long-distance spread of English Ivy, since the seeds within the fruit pass through the bird without damage.

The Ivy can also reproduce vegetatively from broken or cut vines that root easily.

English Ivy attaches to trees by stick rootlets that develop along the stem, which can be up to 12 inches in diameter, and can climb to 100 feet in the canopy, eventually killing the tree by impeding photosynthesis.

It can grow in dense patches in open woodland, forest openings and forest edges, therefore suppressing native tree seedlings.

It can engulf and kill lower branches of trees, due to heavy shade, while the weight of the vines and evergreen leaves causes the host tree to be much more susceptible to blow down from winds or heavy rain, snow or ice.

It may also harbour a plant disease, called Bacterial Leaf Scorch, harming Oak, Elm and Maple trees.

How to Manage English Ivy:

Managing English ivy is challenging but achievable with persistence and a multi-step approach.

Manual Removal:

Small patches can be dug out by using a shovel. This is most effective when the soil is moist.

Gloves and protective clothing are recommended since the sap can cause a reaction in some people.

Do not put plants in compost or municipal green waste; put in garbage instead.

Smothering:

Small or larger patches can be covered with a tarp or cardboard to block sunlight.

Herbicide Treatment:

Older leaves have a waxy coating that resists herbicide. Spraying young leaves in spring is more effective.

You can also increase the effectiveness of herbicides by applying it to cut stems. If the ivy is growing on a tree, cut the stems at ground level and treat, being careful not to apply herbicide to the tree trunk.

Use herbicides only as a last resort, following local regulations to minimize environmental harm.

After removal, replant the area with regionally appropriate native plants and monitor it for several years.

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 choice would be Wild Strawberry (Fragaria virginiana).

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

For more information visit www.ontarioinvasiveplants.ca or www.ontarioinvasiveplants.ca/resources/grow-me-instead

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