This evergreen vine is widespread in western Washington, both as an intentionally planted ornamental and as an invasive plant in woodlands and parks throughout the region.
Legal status in King County, Washington
The four cultivars of English Ivy that have been shown to be the most invasive in the Pacific Northwest are Class C noxious weeds on the Washington State Noxious Weed List: Hedera helix 'Baltica', Hedera helix 'Pittsburgh', Hedera helix 'Star', Hedera hibernica 'Hibernica' (see below for pictures). Hedera hibernica is also called Atlantic or Irish Ivy but is very similar to English Ivy and is generally called English Ivy by most people.These invasive cultivars of ivy are on the non-regulated noxious weed list in King County. Property owners are not required to control these species.
The King County Noxious Weed Board strongly encourages control of English Ivy where possible and containment of spread if control is not feasible. Also, planting English Ivy is discouraged and it is recommended that non-invasive alternatives be used to reduce further negative impacts of this plant in King County.
Impacts and distribution
English ivy and its close cousin Atlantic or Irish ivy are well-known European vines that have been widely used in North America landscapes. Because this type of vine is evergreen and well-adapted to the mild Pacific Northwest climate, it grows all year round in western Washington and can out-compete many other plant species. This aggressively spreading vine can cover everything in its reach and has no natural checks and balances to keep it under control.
In the understory of forests, English ivy spreads over the ground and crowds out native wildflowers, ferns and tree seedlings. Ivy mats often host pest animals such as the Norway rat. Also, because ivy roots are shallow, thick mats covering hillsides can increase problems with slope failure as water runs down under the ivy and entire mats of ivy and soil slide downhill. On walls and fences, ivy rootlets work into the wood and mortar and can cause structural and aethestic damage.
When English ivy is allowed to grow up tree trunks it can increase the risk of the trees being blown over in windstorms because of its large mass and “sail effect” of the vines in the canopy. Tree bark is more likely to have disease and rot problems and the tree health can be damaged by reduced access to light when the vines cover the tree’s branches. Although ivy won’t directly poison the tree, it will most likely harm the tree’s health and increase the chance of it becoming a hazard tree.
- Evergreen vine that can trail along the ground or grow veritcally up trees, fences, walls and hillsides.
- Most common type of growth lacks flowers and has dull green, lobed leaves with light veins that grow alternately along trailing or climbing stems.
- Leaf shape and size varies between varieties from deeply to shallowly lobed and from small, narrow leaves to large, broadly shaped leaves.
- Mature form of growth has shiny, unlobed leaves that grow in dense, whorl-like clusters and produce umbrella-like groups of small yellow-green flowers in the fall, followed by dark purple-black berries in the late winter or early spring.
- When ivy vines climb, small rootlets form that exude a glue-like substance to allow the vines to attach to almost any surface.
- Older vines can be tree-like and as much as five inches thick.
Reproduction and spread
English ivy spreads vegetatively outward through its long vines that root at the nodes and climb over any obstacle. Ivy can take many years to mature but when it does, it shifts to forming mature branches that produce berries. The seeds in the berries are distributed mostly by birds such as starlings, European house sparrows, band-tailed pigeons, robins and cedar waxwings. However, the berries have been reported to be poisonous to some birds. Because English ivy is highly shade-tolerant and adapted to a wide range of soils, it sprouts easily almost everywhere seeds are dropped.
Because ivy has been so widely planted, it has spread throughout the Pacific Northwest and has shown up even in some fairly remote and pristine forests. Clearly, intentional plantings are a key factor in the spread of this species in our region.
Physical removal of English ivy vines and roots is often the most effective method of control. Stems are sturdy and lack thorns and roots are also strong and not very deep. These features make ivy relatively easy to pull without leaving stem and root fragments behind. Hand-pulling combined with loosening the soil with a shovel, pulaski or weeding fork will work on most stands of ivy. Older plants have thick, woody stems and roots and will require more effort to remove. However, older stems also will not re-sprout as much so leaving some root behind is probably not a problem.
Ivy growing up tree trunks can be controlled by removing all the vines from the lower trunk of the tree (only as high as you can comfortably reach). Pry stems off with a large screw driver or forked garden tool. Make sure to remove the stems from all around the trunk. Large vines can be cut using an axe or a pruning saw. The upper vines will die if they are not rooted in the ground, although this can take several months. Clear ivy from around the base of the tree as well or it will quickly re-grow up the trunk.
After ivy is removed, make sure to mulch the area to resist re-invasion by ivy and other weeds. For large areas, it is helpful to put in native or other desirable plants to help reduce erosion and long-term weed problems. Before planting, it is a good idea to wait at least a few months or until spring to watch for re-sprouts or skips since they will be easier to see and pull while the area is still clear.
Ivy vines and roots can be balled up or rolled up like a carpet and left to rot. Turning the pile every few months or so can help keep stems from re-rooting. Piling the ivy on a tarp or other surface can be less risky but it will rot more slowly. If this isn’t practical, ivy can be disposed of as yard waste.
Other methods of control including chemical control are not as easy as physical removal and often results are not as good. However, for large areas or where pulling is not an option, it may be cost-effective to consider other options.
Foliar treatment of ivy is difficult due to the thick, waxy coating on ivy leaves. Leaves are most susceptible to herbicide treatment when they first appear, so early spring treatment or cutting first and treating fresh re-growth will increase effectiveness. According to Oregon State University Extension, spraying with a 2 to 5 percent solution of either glyphosate or triclopyr on a sunny winter day can be very effective. Winter spraying also reduces damage to native plants that are dormant. The same reference reports that cutting woody ivy stems and applying either 2 percent 2,4-D or 25 percent glyphosate solution to the freshly cut surface is effective. Herbicides should only be used according to the directions on the product’s label in order to maximize results and minimize health and environmental impacts. Make sure to take all precautions on the label and to follow local, state and federal regulations regarding herbicide use.
Additional information on annual english ivy
What to do if you find this plant in King County, Washington
Because english ivy is so widespread, property owners in King County are not required to control it and we are not generally tracking infestations. We can provide advice on how to control english ivy, but there is generally no legal requirement to do so.
English ivy photos - click thumbnail for larger image