North Quadra

GARDEN THUGS . . . . English Ivy

Many people continue to plant English ivy [Hedera helix and H. hibernica] in their gardens, unaware that it is a non-native plant that invades our woodlands and forests with devastating effect. It outcompetes natives, reduces numbers and kinds of other plants and impairs the land’s ability to support wildlife. It is so destructive that many jurisdictions, including Washington state, list it as a noxious weed. Saanich has been urged to list it also, but has not yet acted. Locally, Swan Lake-Christmas Hill Nature Reserve is infested with ivy along the trails.

When English ivy climbs into trees, it may weaken the host tree by shading out deciduous foliage during its growing period, preventing the normal contact of bark with air and microorganisms, and acting as a sail when the wind is blowing, which contributes to blow-down. It is shallowly rooted, so it is ineffective for erosion control, and may actually contribute to erosion problems. Heavy infestations can provide shelter for undesirable pests such as rats.

Ivy contains chemical compounds that may irritate the skin. Eating the leaves can harm browsing animals.

English ivy can grow 9-10 months of the year in our area, which is one factor that allows it to dominate in wild areas where there are no gardeners to keep it under control. It has an interesting life history. The attractive leaves for which it is planted are juvenile forms. When it climbs, or sometimes when it has been growing on the ground for a long time, it produces larger, unlobed mature leaves. It then begins to flower and set berries. It blooms in the fall, and matures nutritious fruits in early spring when other foods are scarce. Birds eat the berries and excrete the seeds, all ready to grow in their own little fertilizer packages.

Control

Control of English ivy is difficult. Herbicides do not penetrate well because of the waxy surface of its leaves, and it is tolerant of many of the most commonly used. Hand-pulling is a more effective method, but requires commitment—the writer has been pulling ivy annually from one area for 17 years! Even the tiniest piece of root left behind in the soil will continue to send up shoots. Theoretically repeated pulling will exhaust the plant’s nutrient reserves and it will then die, but as my experience shows, it is very robust!

Do not try to compost English ivy. After it is pulled it must be removed to a place, such as a patio, where it is not in contact with soil. It will dry out and die after about a week if the mass is not so large it retains moisture. It can also be packed in black plastic garbage bags that are placed in the sun and rotated so that all plants are heated.

Last Words

If you don’t have English ivy in your garden, don’t plant it. If you do have it, control it.

English ivy’s role in gardens is as a ground cover. Some native plants that can carpet the ground include wild strawberries [Fragaria spp.], fringe cup [Tellima grandiflora], longleaf Oregon grape [Mahonia nervosa] [that’s the low-growing of the two species most commonly seen in this area], redwood sorrel [Oxalis oregana], kinnikinnick [Arctostaphylos uva-ursi], bunchberry [Cornus canadensis], vanilla leaf [Achlys triphylla] or false lily-of-the-valley [Maianthemum]. Horticultural plants that can do the job and are more easily kept under control [Please! No periwinkle!] include deadnettle [an ugly name for a small creeper with variegated leaves and pink or white flowers in season, also known as Lamium], some hardy geraniums, London pride, lavender, rockcress, ornamental strawberry, some forms of cotoneaster, lithodora, and so on. Consult such resources as the Sunset Western Garden Book, or your favorite nursery for other ideas.

For more information, Saanich has a brochure about ivy that is available at the Municipal Hall.

	Global Invasive Species Database
	NO Ivy League (Oregon)