Tuesday, August 18, 2020

Thoughts on Ivy in Italy: Problem or Part of the Scenery?

Examples of ivy invading trees in winter, near Bergamo.Examples of ivy invading trees in summer, near Bergamo.
Left: Examples of ivy invading trees in winter, near Bergamo. Right: Examples of ivy invading trees in summer, near Bergamo.


We are obsessed with ivy, Hedera. In our opinion, ivy is seems rampant in Italy. If all ivy were removed in Italy, we fear Italy would collapse – ancient ruins, fences, and perhaps, even people – without the binding power of ivy. Okay, a bit of an exaggeration you say. Is ivy really that bad in Italy? We thought so and to challenge the idea, we posed four questions:

  • Question 1: Do Italians consider ivy offensive to look at when running rampant?
  • Question 2: Is ivy invasive in Italy?
  • Question 3: Are we doing more harm than good when we remove ivy?
  • Question 4: Why are we obsessed with ivy?

The answers we found surprised and calmed us a little. TL;DR answers:

  • Answer 1: No, not really.
  • Answer 2: No, at least not at a level that causes significant economic impact.
  • Answer 3: It depends on how it removed and how much ivy there is.
  • Answer 4: We were conditioned to dislike ivy from our years living in Seatte, where it was drummed into our heads that ivy is invasive.

In the remainder of the post, we provide some evidence and personal observations that led to these answers.

The roots

Ivy – commonly called English Ivy – is a woody evergreen perennial native to northern temperate and subtropical zones of Asia and Europe. According to IPCW Plant Report, ivy was introduced in North America by colonial settlers from the United Kingdom; they were bringing a little piece of home with them as was a common custom.

Ivy has old roots in Western culture. Theophrastus (c. 317 BC – c. 287 BC), the father of botany, described ivy in Enquiry Into Plants (Historia Plantarum) (ca. 314 BC). He writes “Wherefore it is mischivous to plant this [ivy] against any tree; for it destroys and starves any tree by withdrawing the moisture.” Even Theophrastus was on to ivy. [p. 277 of Enquiry into plants, translation by Sir Arthur Hort, 1916]

A page from a translation of Enquiry Into Plants: Theophrastus was on to ivy.
A page from a translation of Enquiry Into Plants: Theophrastus was on to ivy.

Ivy can grow in different soil types and once established is drought tolerant. There are two forms to ivy: a juvenile and an adult form. During its juvenile phase, ivy spreads by vegetative growth. The adult form adds the trick of reproducing with berries and seeds. When we see ivy berries, we cringe because it means the ivy has been there for a while as the juvenile phase lasts at least ten years.

Some species and cultivars of ivy are beautiful, especially those with variegated foliage and interesting leaf shapes. You need only head over to the American Ivy Society web site and peruse the different ivies to find yourself thinking about possible indoor or outdoor uses. What about Ivy of the Year 2016, the cultivar Hedera helix ‘Midas Touch’? There are hundreds of cultivars to choose from.

Ivy’s scientific genus name is Hedera. In the genus there about a dozen species, but H. helix and H. hibernica are the two species that are the most troublesome. Note that the American Ivy Society shows cultivars, a cultivated variety of a species like H. helix that is selected for desired characteristics then maintained through propagation.

And while we are talking about names, we should note that Boston Ivy (Parthenocissus tricuspidata) is not a true ivy being part of the grape family (Vitaceae). Boston ivy is pleasant to behold on the wall of a building and rarely found strangling trees – at least that we’ve observed. Also not related to ivy is poison ivy (Toxicodendron radicans).

Advantages of ivy are: evergreen foliage, attracts and supports wildlife, can add an aesthetic touch in gardening, is inexpensive, easy to grow, drought tolerant, aids in nutrient cycling, soil erosion, and animal forage. Note that ivy is not parasitic.

Disadvantages of ivy are: unsightliness when left unchecked, potential damage such as uprooting or breakage of the host tree during storms, competition with native plants and even host trees, and negative impact on under story plants.

To be honest, unsightliness is our biggest gripe with ivy, especially when it runs amok over trees. To be fair, many of the places we observe this are roadside borders and natural areas close to urbanization. These areas are often neglected in the sense that no one takes care of them, but everyone sees and passes through. These throw-away, border areas can be public or private. Often, ivy is planted purposely as a screen or a barrier.

Walking in the highly curated area of Alta Badia (Dolomites) that we are familiar with, we never see ivy. See for example A Hiking Week in the Dolomites, Val Badia and Val Gardena. Walking to Canto Alto just outside of Bergamo, we see extensive patches of ivy. See for example A Classic Bergamo Hike: Canto Alto.

Ivy is simply where people are. Local response (or better yet tolerance) to ivy varies greatly between regions and provinces of Italy.

As a final scientific note, we were pleased to discover that in the Orobanche (Broomrape) family, a family of parasitic plants, there is one species that targets ivy: Orobanche hederae.

Rorschach test

What do Italians see when looking at ivy? We can only offer anecdotes:

  • We were walking with some Italian friends along a wooded street just outside of Bergamo center. It’s a pleasant winter day. We ask them to look at a tree, without leaves and completely smothered in ivy, and tell us what they see. The answer: nothing unusual. What!? We see a tree smothered, struggling and ripe for falling or being blow over and susceptible to disease.
  • We are visiting some friends in the posh Quintino Alto neighborhood of Bergamo and touring the property that their restored farmhouse sits on. We can’t help ourselves and instinctively start ripping ivy out of their trees. They look at us through questioning eyes asking what we are doing. We try to explain how ivy takes over other habitats creating unhealthy conditions. We are not sure they believe us.
  • We walk by a recently cleaned up lot just outside of Città Alta where trees were removed, and the remaining trees trimmed. But the result? The remaining trees (fine specimens at that) where all full of ivy. It’s as if no one gave a thought to remove the ivy.
  • A friend sent us the video by Oscar Farinetti – La fortuna di nascere in Italia – which talks about the great biodiversity in Italy. The video is factual with some exaggerated marketing manipulation of numbers as you might expect from the owner of Eataly. As soon as the video clip ended, we joked that half the biomass in Italy must be ivy.

From our experience, we believe that ivy is not a problem to Italians. It’s not offensive to look at. Rather, it’s a normal part of the scenery. Ivy grows and it gets chopped down, end of story. If ivy takes over a tree, so what. In short, we think that Italians don’t seem to find ivy offensive.

Quantifying US impact

In the book Weeds: In Defense of Nature’s Most Unloved Plants, author Richard Mabey writes “The best-known and simplest definition is that a weed is ‘a plant in the wrong place’, that is, a plant growing where you would prefer other plants to grow, or sometimes no plants at all.” That wrong place can be where you want crops to grow, or where a weed’s dominance adversely impacts wildlife (the growth of native plants) and leads to new problems like increased fire conditions and impeded waterways.

Invasive species – like ivy – have environmental and economic impacts. In the book, Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species, ivy is included and it noted that it is particular abundant in the Pacific Northwest – where we spent our formidable gardening years.

“English ivy grows along the ground and climbs on any plant or object in its path. The dense blanket blocks light and germination of other plants beneath it, reducing local plant diversity. It will grow several stories up the sides of building or into the canopy of a forest, adding weight to trees. Covering tree trunks, ivy can loosen bark and hold moisture against the tree trunk, encouraging fungus and decay. In some cases it provides shelter and food for birds. The berries are mildly toxic though, so few bird species feed on them.”

The Draft Written Findings of the Washington State Noxious Weed Control Board (November 2001) also gives a good overview of ivy, description, history, and impact. These sources don’t give any indication of realy dollar economic impact. To be fair, all environment impacts are ultimately economic impacts and maybe with ivy, those impacts aren’t well quantified because while it’s unsightly, it isn’t impactful as other invasives.

In terms of quantifiable economic impact from invasive plants and animals, the NISC – National Invasive Species Council – Invasive Species Impact on Infrastructure gives some idea of invasives that have tangible economic impacts. Examples include:

  • Invasive grasses, such as buffelgrass (Pennisetum ciliare) and cheatgrass (Bromus tectorum), which literally fuel fires that burn down buildings and damage transportation infrastructure. The National Invasive Species Council describes a well established “feedback mechanism between invasive species and fire”.
  • Formosan termites (Coptotermes formosanu) impact residential, commercial, and federal buildings, including historical landmarks. A 1998 study concluded that Formosan termites exist in more than a dozen southern states, costing an estimated $1 billion a year in property damages, repairs, and control measures ($300 million in New Orleans, LA). The total cost of impacts has likely increased substantially over the last 20 years.
  • Nutria (Myocaster coypus), sucker mouth catfish (Subfamily Hypostominae), and other burrowing invasive species are known to compromise the structural integrity of roads, dams, levees, and bridges - thereby jeopardizing the safety of entire communities. Nutria contributed to a recent levee failure resulting in flood damage in excess of $500 million.

Looking at these impacts (and more examples in the Invasive Plants guide), makes our crusade against ivy feel a bit petty doesn’t it? To boot, the U.S. Department of Agriculture National Invasive Species Information Center doesn’t even list ivy. There must be bigger invasive fish to fry. The U.S. Department of the Interior – National Invasive Species Council however does mention ivy, for example, a notice for an ivy pull at a state park in California. In fact, ivy pull events, are common in the Northwest. The No Ivy League is very active in Portland, Oregon and there is young adult comic book story built around it. Similarly, in Washington, California and other states in the US, the message is clear: ivy is removed because it is not wanted.

We can only conclude that ivy is not desired and has, on balance, a negative environmental impact in some areas of the US, but it’s not as serious as other invasive plants. The US National Invasive Species Council wasn’t kicked off in 1999 over ivy outrage, it was over concerns about ants and termites, grasses, rodents, fish, clams, and other species.

A word about terminology. The Invasive Plants guide has the interesting twist when talking about natives and invasives: “All ‘native’ dominants from ponderosa pine to the American bison and Canada gooes were once successful invasives”. The guide also has this wisdom to keep in mind: “All invasives are aliens but not all aliens are invasives”.

Beyond the US

In the EU, the European Commision List of Invasive Alient Species of Union concern (2016 - 2019) list species it’s keeping an eye on. Ivy is not there. The commision’s well-produced brochure does interestingly list a lot of aquatic plants and hogweeds, Heraculeum mantegazzianum, H. persicum, and H. sosnowskyi. And we thought hogweeds were pretty to see when walking in mountain pastures!

In Italy, the Italian Legislative Decree on invasive species (2017) is the statement of compliance dealing with the same EU list, and obviously no ivy is included.

On the global level, the Global Invasive Species Database at least has Hedera helix as an entry. Unfortunately, they don’t list how invasive they consider it. We can at least say that ivy isn’t on the 100 of the World’s Worst Invasive Alien Species. (We were almost rooting for ivy not to be on the list.) Instructive is what is on the list: insects, viruses, algae, aquatic and terrestrial plants and animals. Again the takeaway is that ivy is a concern, just not of high concern.

After casting about here and there in official documents looking for at least a mention of ivy, it occurred to us, that maybe because ivy is native to Eurasia that it – in its natural state on undisturbed land – would naturally be kept in check. Furthermore, the ivy that we are complaining about is ivy that is in disturbed areas. Following this line of thought, this means that what we are really complaining about disturbed areas that are not maintained, and nothing more. Ivy thrives in disturbed areas and much of Italy is for better or worse, disturbed area, at least around population centers. We should not be blaming ivy but blaming the disturbers: us.

Word games

Looking at the Italian language Hedera Wikipedia entry, you will not find one use of the word invasivo/a (“invasive”) or any related words. In the English language Hedera Wikipedia page, at time of writing you’ll find eight uses of the word “invasive”. Even at the level of language, the association of ivy as invasive in Italian just isn’t there.

Not super scientific and widely cautioned against, we can look at Google Ngram Viewer to see if we can say something more about word relationships. Let’s do two searches:
  • Search 1: Input “ivy, invasive” from 1920 to present in the “American English (2012)” corpus.
  • Search 2: Input (in Italian) “edera, invasiva” from 1920 to present in the “Italian (2012)” corpus.

The interesting trend revealed by these searches is not the absolute numbers, because those are difficult to compare, but the cross over when the percentage of the “invasive” term crossed that of the “ivy” term. In the American English corpus that crossover happened in 1980, while in the Italian corpus it happened in 2003. Interesting, but what does it mean? Italy is 20 years behind English-speaking countries in terms of demonizing ivy? We’ll have to leave it at a curiosity at this point.

Fun with Ngram viewer. English terms "ivy, invasive".Fun with Ngram viewer. Italian terms "edera, invasiva".
Fun with Ngram viewer. On the left English terms "ivy, invasive". On the right Italian terms "edera, invasiva".

To pull or not to pull

Ivy in the US is particularly invasive in the Pacific Northwest – and our ivy-vendetta is learned from our years spent in Seattle. From weekend to serious gardeners, Northwesterners have been trained that ivy is invasive and not to plant it. Here’s a typical example of the press ivy gets, this from the Seattle public radio station KUOW titled Rip the ivy out of your yard right now. Seriously.

Besides the obvious environment impacts listed elsewhere in this post, there are some philosophical reasons we don’t like ivy:
  • Using ivy is a quick fix to a problem that could be solved with different plant choices. Ivy is a quick spreader and climber and that appeals to the just-get-it-done gardener. Rather than wait and do things correctly, corners are cut, and ivy enters the mix. And ivy is cheap.
    • We had a Seattle neighbor who let ivy invade a 30+ foot cherry tree to the point that the tree eventually had to be removed due to disease as it was considered dangerous. After many years of looking at said eyesore tree, we got up the courage to ask why the ivy had been left to fester. The answer was practical: our neighbor liked the fact that the ivy blocked the view of other neighbors.
  • Rampant ivy speaks to us of decay and neglect. It doesn’t take much to keep ivy at bay, we know, we had to work to keep it under control in our yard for years. The idea of neglected, “throwaway” areas is something we hate. (We hear you: form our own ivy pull squad. We took a step in that direction and recently purchased pruning shears so when walk around Bergamo we can be ready.)
  • From a purely visual point of view, trees or spaces overrun with ivy look awful.

To pull or not to pull ivy? Specifically, does it hurt the environment to remove ivy? Is the habitat or food source of insects and animals adversely affected?

Curiously, we found lots of (well-reasoned) caution when it comes to ivy removal that is British based, for example:
  • The Royal Horticultural Society says that you don’t need to always control ivy.
  • The BBC report Five reason why ivy is important cites some compelling reasons to leave non invasive ivy alone including fact that ivy can provide late-season food shelter for some insects and animals and can keep building warmer in winter and cooler in the summer.
  • The Arbtalk forum thread concludes with this on removal: “it depends”.
  • The article Ivy – Boon or Bane? points out that there is little quantitative evidence to determine the true impact of ivy in the British landscape (specifically on trees).

It could be our personal Internet search bubble, but we just couldn’t find much sympathy in the US for ivy as shown in the examples above. We found one measured response in the article If I Pull Invasive Ivy Down from Trees, Does it Hurt the Ecosystem?: it depends on the impact on biodiversity. Beyond that, it’s pull baby, pull. 

Pulling is the easiest if not most labor intensive way to remove ivy. We like pulling, especially pulling ivy out of trees. In fact, when we see a tree smothered in ivy to its crown, we don’t think “what a lucky tree”? We don’t think of all the habitat and berries that the ivy provides. On the contrary, we think the opposite, of all the insects and animals who are not presented with their normal habitat and food. And the danger to the tree. In short, a neon sign the word PULL lights up in our minds.

Perhaps we can think the difference in point of view between US and Britain regarding ivy in terms of the culture, history, and the sizes of the respective countries. Britain has been living with ivy way before the pilgrims took off and brought it to the US. Also, by our reckoning, there is a strong garden culture in Britain and attentiveness to nature that translates into ivy being effectively kept under a watchful eye and managed. We remember our time in England driving from London to Hastings and then from Hastings to Bath. The number of gardens-for-visit we encountered was mind-boggling; We can't imagine ivy not being much of a concern with so much garden pride and attention. Finally, in the US, vast spaces can become infested with no one’s watchful eye to keep it in check. Perhaps that’s why the the idea of ivy pull gatherings/squads is common.


Here are the questions we set out to investigate with answers, restated with answers. While we still believe ivy can be unsightly as hell, we have softened slightly in terms of why that is the case.

Question 1: Do Italians consider ivy offensive to look at when running rampant?

On average, no. There isn’t the demonization of ivy as invasive in Italy as there are in other parts of the world, in particular parts of the US. It’s not offensive to Italians because they haven’t been beat over the head with public service campaigns against ivy because ivy hasn’t impacted the environment in a significant way.

Regarding the aesthetic appeal and acceptance of ivy – again, when it runs rampant, we can only speculate that it’s part and parcel of being Italian. Ivy exists. Ivy twists and twines through trees, fences, roofs, roman amphitheaters, and Etruscan tombs. And often it is planted specifically. Italians are at peace with ivy. (We are not.)

We would love if our friends, whose property we were touring and ripping ivy out of their trees, would warm up to what we would call good management of their property and trees regarding ivy eradication, but that’s not likely to happen.

Question 2: Is ivy invasive here in Italy?

No, at least not at a level that causes significant economic impact. Ivy doesn’t seem to effect agriculture (be it food crops or wood output). Instead, ivy thrives in “un-productive” spaces, nature adjacent to urban areas and where people frequent.

Ivy is not on the EU/Italy list of invasive species. End of story. We have to trust that the officials have thought about this list a bit.

Question 3: Are we doing more harm than good when we remove ivy?

It depends on how it removed and how much ivy there is. The method you choose for removal will have an impact. Laying waste to a patch of ivy with chemicals is probably not a good idea in terms of the health of the environment. Manually removing ivy is better.

If ivy isn’t invasive (whatever that means in your particular context), it could provide habitat and shelter for some insects and animals and confer some other benefits. In this case, removal may not be necessary – but only in the case that the piece of land/garden/terrace in question is under the watchful eye of someone who can keep the ivy from fruiting and becoming invasive. That’s a taller order than it might seem. We recommend you err on pulling ivy out.

Question 4: Why are we obsessed with ivy?

We are obsessed with ivy because we are aesthetically sensitive to urban / natural environments in a state of decay or neglect. As well, we’ve learned from 20 years in the Pacific Northwest and public service campaigns that ivy is invasive. These kinds of campaigns do not exist in Italy, as far as we can tell.


Here are some of the references and resources we used to write this post.

[1] American Ivy Society

[2] Hedera Wikipedia page (English)

[3] Hedera Wikipedia page (Italian)

[7] U.S. Department of Agriculture National Invasive Species Information Center – Ironically, ivy (“ivy”, “hedera”, “helix”) isn’t listed here. There must be bigger invasive fish to fry.

[8] U.S. Department of the Interior – National Invasive Species Council – Ivy is mentioned, for example, an ivy pull at a state park in California.

[9] Draft Written Findings of the Washington State Noxious Weed Control Board (November 2001) – A good overview of ivy, description, history, and impacts.

[11] https://www.invasive.org/gist/moredocs/hedhel02.pdf - a good guide to removal and costs in time

[12] https://www.portlandoregon.gov/parks/47820 - Portland, Oregon no ivy league, could we imagine something like this in Italy?

[13] https://www.portlandoregon.gov/parks/article/201781#whyH. hiberna is the dominant plant; there is a ploidy different with H. helix.

[14] https://wildlife.ca.gov/Conservation/Plants/Dont-Plant-Me/English-Ivy

[15] https://www.cal-ipc.org/resources/library/publications/ipcw/report55/ - California Invasive Plant Council.

[16] https://www.fs.fed.us/database/feis/plants/vine/hedhel/all.html - Ivy most invasive in the northwest.

[17] European Commision List of Invasive Alient Species of Union concern – Lists documents dealing with invasive species from 2016 – 2019.

[18] Italian Legislative Decree on invasive species (2017) – The statement of compliance with EU invasive species.

[19] 2015 Effect of Manual Ivy Removal on Seedling Recruitment in Forest Park, Portland, OR. American Journal of Undergraduate Research

[20] If I Pull Invasive Ivy Down from Trees, Does it Hurt the Ecosystem? – Answer: it depends.

Photo Gallery

Examples of ivy in trees in and around Bergamo. There are a lot of beautiful places around Bergamo and we are only showing these examples of ivy to illustrate a point about how ivy can invade areas.

Summer - A grove of pines with ivy removed in Almè.Summer Ivy - Bergamo - Via Felice Cavagnis.Summer Ivy - Bergamo - Via Felice Cavagnis.
Left: Summer - A grove of pines with ivy removed in Almè.
Center and right: Summer Ivy - Bergamo - Via Felice Cavagnis.

Summer Ivy - Bergamo -Via Colle dei Roccoli.Summer Ivy - On Way to Canto Alto.Summer Ivy - On Way to Canto Alto.
Left: Summer Ivy - Bergamo -Via Colle dei Roccoli.
Center and right: Summer Ivy - On Way to Canto Alto.

Summer Ivy - On Way to Canto Alto, a fallen tree, due to ivy?
Summer Ivy - On Way to Canto Alto, a fallen tree, due to ivy?

Summer Ivy - On Way to Canto Alto.Summer Ivy - On Way to Canto Alto.Summer Ivy - Parco Sant'Agostino. Ivy knocked back on the tree trunk.
Left and center: Summer Ivy - On Way to Canto Alto.
Right: Summer Ivy - Parco Sant'Agostino. Ivy knocked back on the tree trunk.

Winter Ivy above Ponteranica.Winter Ivy above Ponteranica.Winter Ivy above Ponteranica.
Winter Ivy above Ponteranica.

Winter Ivy above Ponteranica.Winter Ivy above Ponteranica.
Winter Ivy above Ponteranica.

Winter Ivy above Ponteranica.
Winter Ivy above Ponteranica.

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