Introduction

Most people know what common Ivy or English Ivy is. It is the common name for Hedera helix, a member of the Araliaceae (Ginseng) family. Sometimes Hedera hibernica, a very closely related and difficult to distinguish species known as Irish Ivy is also sold under the name English Ivy. Many people have them as houseplants, or have them in their gardens, or see them growing up trees in the forests around them. They are a common garden ornamental still widely sold in stores in a variety of different cultivars that wreak havoc in our natural ecosystems. A lot of money is spent every year on the removal of English Ivy from private and public lands.

One of the reasons that Hedera helix and Hedera hibernica are problem invasive plants is that they are capable of invading wild forests and disturbed sites alike. Many introduced plants that gain a foothold in our environment do so because they thrive in human disturbance. English Ivy, on the other hand, thrives in a multitude of ecosystems and a multitude of disturbance regimes, making it particularly invasive.

Description of Hedera helix and Hedera hibernica

Leaves & Stems

English Ivy is a trailing or climbing evergreen vine or shrub growing from thin and shallow roots. In its native habitat it even occasionally grows as a tree. It can form a ground cover 10 – 20 cm tall in its juvenile phase but will climb when a structure is available. When it climbs it grows into a reproductive adult phase where it commonly reaches heights of 30 m. When growing in tall conifers it can even reach heights of up to 90 m. Climbing or older trailing branches start out thin but can reach diameters of 10 – 30 cm with furrowed bark when they mature. The bark is green when young and becomes grey with age.

English ivy is a root climbing vine that grows small roots along its length that exude a sticky substance. This substance in addition to the root structures themselves allow them to grasp and cling onto the surfaces they climb.

The alternate leaves are usually 10 cm long and 6 – 13 cm wide on a 1.5 – 2 cm long petiole (leaf stalk). The leaves are 3 – 5 lobed in their juvenile phase but may become unlobed in their adult phase. The leaves may be solid green or variegated in several shades of dark and light green. The surface is a glossy green with light veins while the underside of the leaves are more pale and not glossy.

Flowers & Fruits

Flowers are yellowish-green and very small. They are clustered in groups of 8 – 10 in umbels on the adult stems. The umbels grow in clusters of 3 – 6 umbels per group. The flowers are very rich in nectar and provide an important food source for many birds in their native habitat.

The fruit is a berry 5 – 9 mm long and 6 – 9 mm wide. It is green at first but becomes dark purple-black with maturity, looking somewhat like a grape. Occasionally the fruits of Hedera helix may be orange-yellow in color. The fruits mature through the fall and into winter and each contains 2 – 5 seeds that are each 5.7 by 3.7 mm in size.

Toxicity

The berries and to some degree the leaves are mildly poisonous to humans and animals. They can also cause contact dermatitis in sensitive individuals. Dermatitis usually only happens to those with a specific allergy to the Araliaceae family or the closely related Apiaceae (Carrot) families.

Distinguishing Hedera helix and Hedera hibernica

Recent studies have indicated that as many as 83% of the populations in Oregon, Washington, and British Columbia may in fact be Hedera hibernica and not Hedera helix as was previously thought. The two species are incredibly difficult to tell apart aside from slight differences in highly variable characteristics. As a result, taxonomically there has been some debate as to whether H. hibernica is a distinct species or simply a subspecies or even a variety of Hedera helix. Hedera hibernica should probably be considered a subspecies because they are virtually impossible to tell apart unless you are a trained botanist. Genetic or microscopic analysis is often required to tell the two species apart.

However, if you have enough experience seeing both species there are some subtle differences that will help you determine the species. But keep in mind that morphological features like leaves and smell are variable and subjective so these alone cannot be relied upon if you require more certainty in your identification. Having said that, the main distinguishing factors are as follows. The leaf veins on Hedera helix are more pronounced and whiter in color than those of Hedera hibernica. Hedera hibernica also has a slightly larger leaf that is usually a slightly lighter green than Hedera helix. Some people claim that Hedera helix smells slightly musty while Hedera hibernica smells somewhat sweet and is more resinous. Apparently, the berries of Hedera helix may at times be orange in color instead of the purple-black that both species usually are.

The one reliable distinguishing characteristic is difficult to use if you are not educated in plant identification. This is the fact that the Hedera species can be differentiated by their trichomes (hairs) on the leaf surfaces. This requires a strong hand lens or a dissecting microscope to view properly. Hedera helix trichomes are erect, bristly, and 0.75–1.062 mm in size. The trichomes of Hedera hibernica on the other hand lie parallel to the leaf surface and are 0.4–0.875 mm in size. The orientation and size of the trichomes are the only truly reliable distinguishing factors that I was able to find in my research.

Native Distribution

Hedera helix is native to Eurasia from Ireland south to Portugal and northern Africa and east to Scandinavia, Turkey, Ukraine, and Iran. It is quite tolerant of cold winters down to -23 Celsius. It prefers cool, moist deciduous or mixed forests in its native range.

Hedera hibernica is native to the Atlantic coast of Europe. It is less cold-hardy than Hedera helix so its range is more limited. It prefers cool, moist deciduous forests in its native range.

Human Uses of English Ivy

Hedera helix and Hedera hibernica are widely used as ornamental vines both indoors in hanging pots and outdoors in gardens. The use of Ivy is widely promoted by horticulturalists and amateur gardeners and it remains a very popular garden plant throughout North America, despite knowledge of its invasiveness in our region.

English and Irish Ivy are sometimes used to grow on the side of buildings where they provide aesthetic qualities as well as some insulation. Although they can also cause minor structural damage.

The leaves and berries of Hedera helix are sometimes used in herbal medicine as an expectorant for coughs and colds as well as bronchitis. They are said to reduce the swelling and blockage of the airways, reduce bronchial swelling and help bring up mucus from the lungs. Some herbalists also recommend it to help treat liver, spleen and gallbladder disorders as well as gout, joint pain and swelling, and scrofulosis. Some herbalists recommend a wash made from the leaves as a means to treat sore or watering eyes.

Habitat Types Where English Ivy is Found

English ivy tends to invade forest edges and clearings allowing it to penetrate deeper into the forest over time. It is also found in fields, pastures, cliffs, slopes, and disturbed areas. It prefers deciduous or mixed forests but is occasionally also found in coniferous forests. Its preference for moisture and deciduous plants also make it a common inhabitant of riparian ecosystems.

Hedera helix and Hedera hibernica grow in both shade and full sun habitats. They grow in moderately fertile and moderately but consistently moist soil types. English Ivy tolerates a fairly wide range of soil pH, though 6.5 is an ideal pH for it. Both species are intolerant of drought and salinity.

Distribution of Hedera helix or Hedera hibernica in North America

English Ivy was first brought to the eastern United States as far back as 1727 when it was brought as an ornamental vine. It was first officially documented in Virginia, USA in 1800.

In Canada, Hedera helix has been recorded in British Columbia and Ontario. According to some sources, much of the English Ivy in British Columbia is Hedera hibernica. Both species, however, are very invasive in British Columbia. So far it has not spread elsewhere in Canada though the maritime provinces in particular are likely at risk of invasion.

In the USA, English Ivy is widespread throughout the eastern USA including Missouri, Arkansas, Louisiana, Illinois, Indiana, Ohio, Kentucky, Tennessee, West Virginia, Virginia, Maryland, New York, New Jersey, Washington DC, Pennsylvania, Connecticut, Massachusetts, North Carolina, South Carolina, Georgia, Florida, Alabama, and Mississippi. It is also found in the south in Texas, Arizona, and Utah and in the west in Idaho, California, Oregon, and Washington. English Ivy is also present in Hawaii. It is believed that much of the English Ivy in the Pacific Northwest is actually Hedera hibernica, though both appear particularly invasive in this region.

In Mexico, Hedera helix has been found throughout central, western, and northern Mexico. It has been reported in Baja California (norte), Chihuahua, Coahuila, Nuevo Leon, Durango, Sinaloa, Jalisco, Aguascalientes, Guanajuato, Michoacan, Mexico State, Mexico City, Puebla, Veracruz, Hidalgo, Queretaro, Tlaxcala, Guerrero, Oaxaca, and Chilapas. It is in the southern US on the northern border of Sonora and Tamaulipas so it is likely already there or will be soon. So far it has not been reported anywhere in southeastern Mexico in the Yucatan peninsula area.

How English Ivy Spreads

English Ivy spreads mostly vegetatively through rooting stems or from fragments of stems or roots. Hedera helix or Hedera hibernica can both reproduce sexually by seed when they achieve their adult phase. However, sexual maturity usually only occurs in open or disturbed habitats. Sometimes climbers that are able to achieve a sufficient amount of sunlight also reach a sexual reproductive phase. In forests and riparian zones, vegetative reproduction is far more common.

Birds eat the fruits and spread the seeds short distances this way. Birds in North America that eat the seeds include the European Starling, Stellar’s Jay, Mockingbird, American Robin, House Sparrow, and Cedar Waxwing. Usually, the birds regurgitate the seeds rather than defecate them, however, so this dispersal method only works on short distances.

It is primarily spread through long-distance by deliberate human introductions in gardens as an ornamental vine or ground cover. Sometimes they can spread from the careless disposal of unwanted houseplants or yard waste.

Habitats at Risk of Invasion in North America

Deciduous forests and riparian habitats are particularly at risk of invasion because this is their preferred habitat. English Ivy threatens all levels of vegetation from the ground to the top of the canopy due to its tolerance of both shade and full sun.

Both Hedera helix and Hedera hibernica appear to be particularly invasive in the Pacific Northwest of the United States and British Columbia, Canada. The temperate mixed rainforests present ideal growing conditions. There is also not many native vines in the region to compete for the climbing niches.

English Ivy has often been considered less invasive in eastern North America. The only reason I found for this was a reference to its infrequent seed production. However, it reproduces far more often vegetatively than through seeds anyway so that is hardly a reason to consider it less invasive. In my travels to the eastern USA, I noticed a lot of areas invaded by English Ivy. There are also a lot of other very vigorous native and introduced vines in the region, such as Virginia Creeper and Kudzu, for example. This creates a lot of competition and this, I believe, is the primary reason that it does not appear to be as invasive in the east.

From my experience though, I still saw it behave invasively throughout many areas in Georgia in particular. I also noticed this in parts of North and South Carolina, Virginia, Alabama, Kentucky, and Tennessee. It is considered invasive in some eastern states including Georgia, Kentucky, Alabama, Tennessee, and Washington DC. And despite earlier claims that it was not a threat in the Great Lakes or southern USA regions, recent studies suggest it is becoming an aggressive invader in those regions as well.

Because Hedera helix and Hedera hibernica are both intolerant of droughts they will not invade desert areas. English Ivy is also intolerant of salinity so it will not grow on beaches, in estuaries, or next to brackish waters.

Impacts of Invasion

English Ivy is an aggressive invader that climbs and damages native trees where it becomes established. They cover the trunk and branches of the trees blocking light from reaching the leaves and interfering with the process of photosynthesis. Large trees will slowly decline and eventually die after a period of several years to a decade or more from this. Young trees are particularly vulnerable in that they can be more quickly pulled down and killed by the weight of the ivy growing on them.

Where ivy becomes particularly dense as a ground cover it can create a monoculture. In this state, it effectively blocks out all other vegetation from growing in that location. Because it can live for a very long time (50 to 70 years, with some reports from Europe in the hundreds of years), this can be a real problem for biodiversity.

English Ivy on houses can damage walls and invade gutters creating blockages. It can also pull gutters off the roof and climb under roofing causing leaks. I have seen it climb through walls into the interior of homes.

English Ivy also holds bacterial leaf scorch (Xylella fastidiosa) which is a plant pathogen. This pathogen is damaging to native elms, oaks, and maples as well as a variety of other native and ornamental trees and shrubs.

Potential Benefits of Invasion

The berries do provide a food source for some of our native birds. However, only mature vines in open sunlit areas are capable of providing this food value. Those damaging the forests offer no food source to our native animals or birds.

Methods of Removal of English Ivy

As always prevention is the preferred method of control. English Ivy, sadly like most invasive species, is still widely sold online and in local garden stores. So much so that there is the “American Ivy Society”, a non-profit society “dedicated to preserving the genus Hedera“. As though this invasive species is in need of preservation in the Americas. The irony of that astounds me. Hopefully I am not being too offensive by saying that. But there is not a single species of Hedera that is native to the Americas, and the genus is incredibly invasive on our continent. Instead, maybe they should focus on the preservation of the native species threatened by the genus Hedera.

Moving on, prevention is key. Do not buy or transport any English Ivy. Do not plant it in your yard. Research vines native to your region and plant those instead. If you have an Ivy as a houseplant and no longer want it, burn it or kill it by some other means before disposing of it to prevent it from growing in garbage dumps or yard waste piles.

If you see them being sold online or in your local garden stores please inform them of their invasive status and ask them to do their part and cease selling them. Ask them to instead sell more native species as ecologically friendly garden alternatives to invasive species.

Physical Control Methods

Once already established, however, physical control is always the most effective means to remove English Ivy. Physical control is labor-intensive and time-consuming but it usually causes the least amount of environmental damage.

Removal of Climbing VInes of English Ivy

To remove climbing English Ivy cut the vines near their bases then you can pull the vines down out of the trees. You also need to remove the root or the vine will simply grow back so dig the roots out as well. Roots are easiest to pull after a good rain when the ground is wet. If the ivy is in your yard you can always water the area first before removing the English Ivy. Fortunately, ivy is not very deep-rooted so they are not too challenging to get the roots out.

Occasionally you will be unable to remove the roots of a climbing vine. For example, when they are at the base of a small native tree and you are concerned you will damage or kill the native tree. In this case, you will need to return and repeatedly cut back the stump as it tries to grow. Eventually, without green leaves for photosynthesis, it will die.

Removal of Sprawling Vines of English Ivy

To remove English Ivy that is sprawling as a ground cover, again it is best done after a rain when the ground is wet. Start pulling from the edge of the patch and work your way in from there. Try to get all the roots out which can be challenging because sprawling vines will root in multiple places along their length anywhere the vine itself comes into contact with soil.

If you are looking for a less labor-intensive method and you have a relatively small patch of ground cover in full sun that is 100% ivy you could try solarizing. Put heavy black plastic on top of the vines and weigh it down with rocks. Leave it for 8-10 weeks to smother the plants then remove the plastic and save it for something else. This only works in full sun and is not recommended if native plants are still growing with the ivy.

In all cases of ground cover patch removal, the site will need to be replanted immediately because the bare soil will allow the ivy or other potentially invasive species to invade the newly disturbed area. A replanting program should already be planned and ready to implement immediately upon the removal of English Ivy.

Disposal of the Vines Once Removed

Once the English Ivy has been removed the vines should be burned to ensure they will not propagate elsewhere. Never just dump the vines with yard waste. Yard waste dumping piles are often one of the worst sources of invasive species in our environment. If you are unable to burn them in your area due to fire bans you can put the vines under a heavy tarp or into garbage bags and solarize them. Leave them in a pile under the tarp or in black garbage bags in full sun for 8-10 weeks to ensure they are no longer viable. Then they can be disposed of.

Chemical Control Methods

Chemical applications are almost never an ideal method of control for any invasive species. That is because chemical alteration of the environment often makes the environment more suitable for invasive species than native species. Furthermore, it is often difficult to keep the chemical control method contained so that it does not directly impact any native species during the application process itself. As a result, plots where chemical control is used almost always show a decrease in species richness. On the other hand, in plots where only physical control is used species riches significantly increases.

Furthermore, there are no chemical control methods that effectively target only English Ivy. This means that any application on climbing English Ivy could potentially damage the tree that it is climbing on. Furthermore, even in ground cover patches, the glossy leaves make application of chemicals challenging. Furthermore, Hedera helix is resistant to multiple herbicides.

Chemical control is not recommended.

Biological Control Methods

Biological control involves the use of a predator, herbivore, disease, or some other biological agent to control an invasive species once it is established in the environment. The problem with biological control is that the agent used must be entirely specific to the target organism. This is often difficult to determine since the agent of control is also not native to the environment and could behave differently when released there. Take the example of the mongoose and the rat. The mongoose was released in Hawaii in the late 1800s to help control the rat. To this day there are still rats in Hawaii but the mongoose has helped to decimate many native bird populations. Biological control methods are extremely risky and should only be carried out by professionals after years of rigorous study.

There are currently no biological control methods that specifically target English Ivy. Due to its huge popularity as a garden plant, it is unlikely that one will be developed.

Domestic goats can be a viable option for ground cover patches that are 100% ivy. Domestic goats will eat just about anything, including ivy. This makes them effective at controlling ivy. However, the goat would need to be contained in a fence or on a lead that keeps them only in the ivy patch so that they cannot eat the native species that might be present there since they will eat anything. The roots left behind will however still re-grow so integrated management practices will be required. This includes following up with the physical removal of roots or repeated grazing by goats, coupled with ongoing monitoring.

Integrated Management and Ongoing Monitoring

Integrated management involves the use of multiple control and monitoring methods to control an invasive species. In the case of English Ivy, it mostly involves the physical removal of the English Ivy followed by replanting and ongoing monitoring.

Replanting is Crucial

Replanting of ground cover sites where large areas of English Ivy is removed is essential to prevent the ivy or other invasive species from taking over the newly disturbed ground. A replanting program should already be in place before the removal of English Ivy begins. Native species should always be the preferred choice for replanting. Research native species suitable for that area. If at all possible gather seed stock or cuttings from local plants in your area to ensure you have ecotypes suitable to your area. Otherwise purchase native plants from a local nursery that specializes in ecological restoration to ensure you have the wild types and not cultivars.

Ongoing Monitoring is Essential

Afterwards, ongoing monitoring is absolutely essential. Even if you replant the site and think you pulled all of the roots there will still be root and stem fragments left in the soil that will re-grow. Left unchecked this regrowth can take over your native plants and lead to an entire new infestation given enough time. Yearly monitoring programs should be put in place to ensure that any surviving individuals are removed so that the population is not able to recover. Simply return to the site each spring or summer and pull out any new regrowth that is seen.

References and Resources

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – Lyrae’s Nature Blog Dictionary of Botanical Terms

Fire Effects Information System on Hedera helix https://www.fs.fed.us/database/feis/plants/vine/hedhel/all.html

Hedera helix berries photo from Wikipedia By Petr Filippov – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1894902

iNaturalist Plant Search https://www.inaturalist.org/home

Invasive.org page on Hedera helix https://www.invasive.org/alien/pubs/midatlantic/hehe.htm

M.Strelau, D.R.Clements, J.Benner, and R.Prasad. The Biology of Canadian Weeds: 157. Hedera helix L. & H. hibernica (G. Kirchn.) Bean. Canadian Journal of Plant Science. 98(5): 1005-1022. https://doi.org/10.1139/cjps-2018-0009

USDA Plants Database https://plants.sc.egov.usda.gov/home

Willis, Lyrae (2022).  Plant Families of North America. Not yet published.

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