I wrote the piece that follows while still a horticulturist working for Portland Parks about 20 years ago. It remains largely in its original form with a few additions, corrections and updates. Both plants are still under addressed in the landscape today. While employed I maintained my license as a public applicator of pesticides, a job requirement. I no longer have one, nor do I have a consultant’s license. In many cases herbicides can be an essential part of an effective strategy for the control of an established population of invasive plants. Invasive plants, like these, which are listed on your State’s Noxious Weed List, are there because of the the threat they pose to the environment and their capacity to infect and dominate a landscape, any landscape, across our region. In more than a few cases manual and mechanical methods of control alone are insufficient to ‘control’ the invasion and sole reliance on them will assure the failure of the establishment of a desirable landscape on a site. Herbicide use is thus justified. Large scale restoration projects are often dependent upon it. On a smaller residential property, with commitment and persistence, a homeowner may be successful, but even then they need to understand that there will be a continuing and significant threat of reinfection from surrounding properties, via birds carrying the fruit of Ivies and wind blown seed from Clematis. For some species, especially when the scale of the invasion and property are larger, its use may be essential. For many weeds this herbicide ‘threshold’ is very low before its use is a requirement. In this way scale works for homeowners as their properties and problems are smaller. Too often though properties are neglected and then the buyer inherits a serious problem. Using any herbicide will always have potential adverse effects on the environment, so if you choose to use it make sure you do so effectively. If you choose to use any of my herbicide suggestions, you are on your own. Do your research, understand your problem, to assure that your actions are effective, safe and responsible.
Getting Down to it: Your Viney Culprit is Probably Hedera hibernica, Irish Ivy, or More Rarely H. colchicum
English Ivy, a friend and co-worker announced early on in a then still continuing series of work meetings concerned with various issues of invasive plants, has been a kind of “anti-poster child” for those working in the regional conservation and restoration field. Its spread and control has been the subject of innumerable meetings, proposals and actions both fruitful and not. Eradication is no longer considered a realistic goal by many. The focus, rather, is on limiting its spread and control. Like other exotic invaders and introduced guests now run amok, from diseases to various shellfish and weeds, once a particularly well adapted species establishes a viable population base, it becomes a part of the disturbed novel landscape…it’s here and we’re going to have to figure out how to deal with it. This has always been the way of the world. The difference today is the rapidity with which these changes have been introduced through trade, the peripatetic travels of man (Man in the generic sense) and our never ending appetite for the consumption and disruption of land.
Three different plants have been for years unknowingly bunched together as English Ivy here. Hedera helix, H. hibernica and the most recently identified H. colchicum. As a group, these are the most well recognized invasive exotic weed in the western Pacific Northwest. There is tons of helpful information on these available on the internet, covering its biology, its ecology and various methods of control, yet it remains a daunting and expanding problem today. Brought here early in the settlement of the region and commonly planted around homesites, we suffer from its ‘success’. So easy to propagate you can literally drop it on moist loose soil during our long cool wet season and it will root. For decades it was a ‘bread and butter’ plant for many nurseries here. It fairly leaps across the bare soil, disturbed and undisturbed sites alike. It was a boon for those whose job it was to quickly cover the ground and slow surface erosion on disturbed sites (Its superiority at this has been disproven more recently, but beliefs die hard.) This same characteristic has been its curse as it weaves its dense, tangled mats a foot and more thick across the land. Like all living things it is genetically driven to reproduce, set its prodigious seed and multiply. Like many or most invasive plants, it also possesses the capacity to increase itself vegetatively, rooting wherever even fragments lay in contact with the ground along with persistent long lasting seeds which can lay in wait, accumulating in the soil seed bank.
The two plants Hedera helix and hibernica which comprise the vast bulk of the problematic Ivies here, are sometimes listed as two separate species, while some botanists have subsumed hibernica as a subspecies within H. helix. It is currently understood that 85% of these plant escapees in Oregon are H. hibernica most of the rest are H. helix and a small remainder are a third species H. colchicum. To tell the difference requires a 30-40-power dissecting microscope. Each species has a fair degree of variability in leaf size and shape so it is difficult to rely on that as an identifier. Look closely at young ivy stems and under young leaves, where you may find an undisturbed white fuzz comprised of individual trichomes. Hedera hibernica has flat trichomes, which look like tiny starfish with 5 to 8 rays. The trichomes of H. helix are erect and bristly, with
8 to 12 rays. H. colchica’s trichomes are much smaller, lay flat to the leaf and are scale like with many more rays. Their identification is made harder with time and handling as these tiny structures are distorted. Trichomes grow out from the plant’s epidermal, protective layer. Check this Hoyt Arboretum site for help with determining which you have. The different species may respond to herbicides differently.
Several Ivies, in fact many aggressive invasive weeds of other species, are polyploids, having multiple sets of chromosomes beyond the standard two which is the base quantity for most organisms. Humans have two sets of 23. H. helix is also diploid with the standard two sets, 48 chromosomes. H. hibernica, is a tetraploid with four sets, 96 chromosomes. Polyploids often have thicker, larger leaves, stems and branches, they can also possess more vigor. At least along the western coast of North America H. hibernica is the predominant invasive, while H. helix tends to dominates on the east coast. Why this is exactly so…?
Ivies as a group sprawl across the ground in their juvenile, immature, form. Ivy watchers estimate that after 10-12 years or so hormones are produced that prepare this plant for its mature phase. It continues growing along the ground in the shade of trees or across open ground, until it reaches a tree or a vertical surface and then heads for the sunshine, in its mature phase, but it doesn’t need anything to climb up. This was made obvious years ago to me when an acre of it matured on an exposed bank of the Willamette before we eventually got rid of it. Climbing or simply heaping up on itself on open ground the plant develops mature foliage which is significantly different being larger and less angular while forming thicker gnarly stems. This mature form flowers whether high within trees or atop lumpy ‘mounds’ before ripening its almost black 1-5 seeded berries. Mature woody vines can take on the girth of small trees, though the ‘wood’ is softer than what most of us would consider tree like.
The clusters of black fruit follow and are readily eaten by Starlings, another European import, who may spread the seeds over a relatively large area along the forest edge and about the City. English House Sparrows have been observed feeding on the fruits and their foraging into heavily wooded areas may be responsible for its spread there. The native bird population, is less of a factor. Species, such as Cedar Waxwings (Bombycilla cedrorum), American Robins (Turdus migratorius), Stellar Jays (Cyanocitta stelleri) and Mockingbirds (Mimus spp.) play a smaller role in their spread, these native birds appear to have a preference for native fruits. The same applies to our other native animals. Ivy by displacing the diverse mix of native plants, drives away our native fauna. Ivy appears even less palatable to slugs.
Both Hedera helix and H. hibernica were added to the Oregon State Noxious Weed List in 2010 so that now, long after its arrival and establishment, it is quarantined. Nurseries are no longer allowed to propagated or distributed these within the state. This does not apply to many cultivars even though some argue strongly for their inclusion as reversions are relatively common…others, particularly collectors and specialty growers argue against such bans, stating that these cultivars don’t revert to their aggressive species type. That debate continues.
Ivy removal is very demanding work and, if you are working alone, it can be overwhelming. Cutting it from the trees is difficult enough, removing it from the ground makes that look easy. Its tough pencil thick stems root and run across the ground endlessly, each one that you pull up exposing several more that you missed when working on a mature ‘patch’. This interconnected heavy mat can also be of benefit when removing. The sprawling stems reach out in all directions, heaped and knotted making beginning difficult, but being of some advantage once you have enough of the mass loose and ‘rolling’, then its weight and reach work for you…, like rolling a log or a giant rug. It is best to take advantage of gravity and start at the top of a slope. This method tends to tear up the entire mat as a piece. Gravity is your friend, use it! If you can haul the massive rolls away, please do. They don’t have to be too big before that is only possible with our good friends winch and hydraulics. If you can’t remove it, most of it will die and eventually rot. Be patient and save some part of your back for more enjoyable pursuits.
Most of the time when help is available the Ivy is simply cut from the trees to protect them from the immediate threat, engulfing the tree’s crown, depriving it of light, the branches eventually dying, or adding so much weight and bulk to it that storms and gravity bring them down. Unfortunately, cutting the Ivy from the lower trunk is a short term fix. You will find yourself every few years returning to repeat the process. If the infested area is very large you better find some more help, otherwise the appreciation of those who follow you will be rather limited.
Sandy Diedrich, for years the brains, energy and heart behind Portland’s Forest Park Ivy Project, compiled a great deal of information on the growth, spread and manual control of English Ivy. Much of what I have described here comes from conversations with her as well as my own experiences. She shared it with any who would listen including innumerable student groups whose aid she enlisted in the work on the ground at Forest Park and as summer interns. She also worked tirelessly to get it listed on the state’s Noxious Weed List with like-minded land managers and conservation groups. Sandy promoted her idea of ‘lifesavers’ for several years before she passed in 2007.
Lifesavers are an alternative tactic to the annual or biennial ritual of cutting the clingy stems from the trunks. It involves more work up front, but much longer lasting results. Cut and remove the Ivy, including the main root of each plant, within a 6’ radius or greater of the tree. At this distance, new growth will be redirected randomly away from the tree. A big believer in documentation, Sandy showed me photos of new growing tips curving 180 deg. away from the trees and cut Ivy ends. Less than six feet and the Ivy senses the tree and makes a bee-line for the trunk. Why this happens, she isn’t sure, speculating that there is some hormonal reaction in the plant. Many ornamental climbers exhibit a similar tendency as they grow up for the light (phototropism) while growing towards an uncontacted support before clasping or twining around them. Lifesavers will afford you more time to come back later to gradually and methodically, remove what remains between the rings.
Another helpful bit of practical knowledge she shared is how much of the root system you must get out to be effective. The younger the plant the more important it is to get as much root as possible, fortunately, although seedlings may be numerous, their new roots pull up relatively easily. As the plants mature and the roots caliper up, just getting the woody main root without following all of the lateral roots will work. This will help reduce the amount of soil disturbance and damage to the remaining desirable plants.
Another aside she learned was that often times simply by removing the mat of Ivy many perennials, which were lying their waiting beneath are ‘released’ and begin to grow reducing the need for so much planting and establishment yourself. Of course this all depends on how ‘disturbed’ the site was before the Ivy took over. If the native understory was removed and weedy species established before the Ivy came along, natives won’t magically appear on their own.
Very often either the scale of the task or our own physical limitations get us thinking in terms of less demanding alternatives. Herbicides, for reasons of cost and limited labor, became an area of focus when people became more serious about the removal of Ivy from the landscape.
Prior to its listing as a noxious weed, there was relatively little organized experimental work done with herbicides to control of Ivies, in part because it was still an economic ‘crop’ of the nursery industry and widely planted by many. Control efforts lacked focus and anecdotal evidence gave landscape workers the feeling that any efforts would be futile. Cut it and it grew back. Spray it as you might most any other undesirable woody plant and its thick waxy cuticle sloughed it off with hardly more than a chlorotic ‘burp’. Traditionally much of our spraying occurred during the spring and early summer when weeds were most problematic and the Ivy was growing with such vigor that the translocation of an herbicide down to the roots was difficult. We’ve since learned that many such vigorous weeds are better sprayed in Fall when the growth rate is reduced and the herbicide is taken up more readily.
Locally, within the City bureaus tasked with care of the public landscape, staff began looking more systematically at how we might be more effective using herbicides to control Ivy. One thought was spraying in fall and winter when metabolism was slowed and there was less movement of water up from the roots and when a non-selective herbicide like Round-up would not damage the remaining, but dormant, native perennials. Round-up contains a surfactant to help it penetrate the cuticle and surface cells of most foliage, but a co-worker in the Bureau of Environmental Services doing large restoration projects began experimenting with additional surfactants added to the mix to address the unusually thick cuticle of English Ivy. A range of concentrations were tested in the field and the most efficacious mix was settled on. Basically this is the highest concentration permitted on the label for the Roundup (Glyphosate), we generally used Rodeo which is the same herbicide without the proprietary surfactant and added another surfactant. Since then others have been replicating this effort with good success spraying in early fall and winter. 90-95% kill was attained. Follow-up is required and vigilance in monitoring as well both because of the remaining seeds on site and the likelihood of re-infection from off site. If you choose this method remember that the Roundup will penetrate and kill the desirable plants on whose foliage you spray it!
If you want to try this method, talk to someone who has done this successfully if you can and read the label! It will not tell how to get rid of English Ivy. Many people use what they remember used to work on other weeds or do what someone told them to do. Federal law states very specifically that the label is the law. It will give you guidelines so that you don’t over apply and cause damage that you never intended. . Use the highest recommended concentration. We add a non-ionic surfactant, a product called Scythe, in the highest concentration suggested on its label to help penetrate the waxy cuticle that covers the surface of Ivy leaves (Surfactants break the surface tension of water causing it to spread and penetrate, not bead up on the surface. In a sense it makes water ‘wetter’, may dissolve some of this wax, working much like a soap when you are washing dishes breaking down fats and oils.) Surfactants are classified as inert because they do not directly cause the plant’s death. This does not mean that it is benign to all life. In fact the surfactant that comes in regular Roundup is what makes it toxic to amphibians and will cause your eyes to burn if it contacts them, much like any soap. If your concentration is too weak or if rain or irrigation follows too closely, you have just wasted the chemical and your time allowing it to move into the environment without any of the expected benefit. After spraying, be patient! Ivy has very substantial foliage and, depending on the growing conditions, can take a very long time to show signs of decline and death especially in the Fall-Winter when the plant’s metabolism is slowed. Don’t go in and cut it back too soon. Let it work.
A removal/ reclamation project I began in the fall of ’10 on a steep bank of the Willamette combined several techniques. First with a large crew we spent a day cutting a continuous line down through the Ivy mat to the ground and began manually peeling it back rolling it down the slope. This was growing on rock, the rip-rap, where it was closer to the river. This area lies at and below the average high water mark of the river, an elevation not reached since the big flood of ’96. These heavy ‘bundles’ were winched up and loaded out with a boom truck. Late the following September I sprayed the remaining portion higher up the bank to the viewpoint (This was done in compliance with our policy concerning herbicide use near waterways at the behest and with the support of the National Marine Fisheries folks. Ours was the first such policy in the West and served as a model for other regions with Salmon bearing streams.) This eventually left a thick, up to 1’, mat of dead stems to plant through. In late November I began planting with xeric plants, chopping holes in the dead mat. This is a very hot unirrigated site. Fall planting would give the plantings time to get roots established before our annual summer drought period. Each plant required a portion of the mat to be cut and pulled out. As expected there was something less then 5% of the area where Ivy began to grow back the following spring. I was able to remove some of this manually without disturbing the new plantings, the rest required a careful reapplication of herbicide. The following fall I did some replanting to fill in open areas and in response to vandalism. Festuca rubra commutata was sown this second Fall, to help crowd out other weeds that my work would ‘release’.
This project was only partially successful. In our continuously changing urban world no landscape is ever ‘done’ or completely safe from reinvasion. Unfortunately, the removal of the Ivy opened it up to unwanted or anticipated human foot traffic which would occur during large public events on the adjacent site. Things tended to get trampled and I retired. Any site will all require constant monitoring and vigilance.
For those few to whom money is of little concern and time is very short, I once participated in a replanting project in which it was decided to remove the top 18” of topsoil from a several thousand square foot site and replaced it with clean soil rather than risk re-infection of the new plantings. On another large site the Ivy was sprayed following the recommendations and once ‘killed’ trac-hoes were used to rake the long narrow acre site free of the dead Ivy and hauled off by the 12 yard truck load.
However you choose to do it, Ivy removal is not for wimps!
Clematis vitalba…Not to be Confused with our Native Clematis ligusticifolia
If Hedera helix is our familiar ‘poster child’ for invasive plants, Traveller’s Joy, Clematis vitalba, is the new(er) kid on the block, although it is very well established in the Portland area and surroundings today. When I first moved to Portland in ’85 its spread was much more limited. Sadly, so was awareness and with that, there was little organized effort to control its spread. An all too common problem. Today it is found everywhere across the City and is increasingly common on residential properties where it is engulfing landscapes and burying small structures. While it is firmly established and spreading rapidly, it is not widely recognized as a problem by the public. There is also a smaller body of information that has been developed on the particulars of its growth and its response to control measures…but this is changing as various agencies and organizations work to determine the best practices to eradicate or control it on a site.
Within the City system Clematis (Generally pronounced klem-A’-tis.) was a bad word. Those concerned with its control are often unaware of the hundreds of desirable species and varieties available, with a little looking, to gardeners in the Maritime Pacific Northwest. To many the name conjures up a particularly nasty weed. The limits of their knowledge lead them to think gardeners are crazy for planting such weeds in their yards assuming them all to have weedy tendencies. To the untrained eye of those still living in a simple world inwhich all Clematis are ‘one’ the difference between Clematis vitalba and its more well behaved kin is ignored.
Gardeners, who often pronounce it KLEM’-a-tis, particularly those currently under the spell of this large and appealing genus, can often list the several vitacella cultivars, large flowered hybrids, the increasing number of low ‘herbaceous’ forms becoming available and the confusing array of species, that they have tried or have developed their own unrequited relationships with. As a person easily consumed by my own obsessions, I would not be surprised if many, if not most, home gardeners were unaware of the threat that C. vitalba poses to their own gardens and our regional landscape. For those of you unfamiliar with this genus, or even if you are, you should plan a visit or two to the Rogerson Clematis Garden at Luscher Farm Park south of Lake Oswego. Check out their website.
We have all seen this plant dominating the median strips lining major transportation corridors. In many inner city areas, where left on it’s own it is burying the landscape, overwhelming Forsythia, Rhododendrons, rose, hedge and Cherry alike in nondescript and little cared for yards…launching its persistent attack into our own gardens from its large ‘fluffy’ seed heads. The delicate and lacy appearance of their newly unfolding leaves belie their true character.
Clematis vitalba was brought to Oregon as an ornamental to grace our gardens. It has been used to create hybrids to lend them some of its vigor. Uncontrolled it can climb as high as 100′ into the crowns of trees. We don’t normally think of plants possessing the capacity for speed, but this one has it, a capacity we can see clearly by cutting it back in Spring and leaving it to its own devices as it explodes back from its tangle of stems on the ground and its supporting root system….Its seeds possess the capacity to germinate and grow in the most difficult to access locations, such as within other prized plants, deep within hedgerows and shrubs. Before very many years pass it can bury your landscape beneath its light devouring mass and, much like Ivy, lend its bulk to tree crowns increasing the likelihood of their collapse. Like many other garden escapees, among them Purple Loosestrife and English Holly, this one has found fertile ground here. Its clusters of small white flowers offer none of the fragrance that some of the similarly flowered species do and its puffy seed heads are a promise of exuberance and weeds to come. To complicate matters it appears very similar to our native Clematis ligusticifolia
Our native possesses no where near the vigor of the interloper generally limited to 20′, occasionally reaching to 50′. There are differences in leaf, the flowers and seed heads as well, at least superficially. The plants are dioecious, either male or female, although different plants can become entwined. Close inspection of the flowers is required to definitively tell our native from the interloper, the native species having imperfect flowers either male, staminate, or female, pistilate, seed forming on only the female flowers. It has 5-7 commonly, but can have even more leaflets. The native is primarily found east of the Cascades, though occasionally on the west side. See link for a more complete description.
C. vitalba has perfect, complete flowers with all their parts, opening in summer, overlapping the native species bloom period. As perfect flowers all are capable of producing fertile seed. Their leaves are composed mostly of 5 leaflets, sometimes 3 on younger shoots.
Within less groomed areas of Parks and along Terwilliger Blvd. C. vitalba hangs from the trees like the torn and dusty drapes and cobwebs of a Gothic horror house, their puffy seed heads loosening their millions of seeds on whichever breeze can reach them. Clambering over Ivy and shrubs they climb high into trees. Some of the heavy stems hang like ship’s hawsers, 2” in diameter, making fast the gathered trees to the sloping and heaving earthen dock. Their ropy stems display a shredding, peeling, bark more prominent on larger stems. The stems have knobby nodes spaced along their length from which rooting and branching occur. A fast grower, its medium green leaves lay thickly on top of anything else in the understory. It is even capable of burying the Ivies, as it can outgrow anything here in its search for light. The Ivy tolerates it biding its time as it waits in the shade, the Clematis having a greater need for sunlight. Many other plants, deprived of light, die. The two form a particularly deadly team.
Clematis vitalba is internationally recognized for its ability to invade even undisturbed sites. It is firmly established in Oregon and Washington and has become a serious invader elsewhere in the world. The maritime Pacific Northwest would seem ‘ideal’ for this. One conservation organization gives it a 4.5 on a scale that runs from 1 to 5, with 1 being a weed in cultivated areas only and 5 being so dominant that it out competes natives to the point where nothing else may grow on the ground. This plant is a survivor. One researcher found that it can produce 17,000 viable seeds per year per sq. meter of canopy! As a plant that has the vigor of a Wisteria once it’s established, you can imagine how much seed one plant can produce.
The text included with the Oregon’s Noxious Plant List reads:
‘Threat: Like English ivy, it is one of the largest invasive species threat to trees • Blankets shrubs and trees, eventually causing them to collapse • Grows along ground in layers that are several feet thick, preventing growth of native vegetation • Spreads quickly along river margins, but will establish in any area not managed.
Spread: Can grow five to seven times faster than ivy, with each stem capable of producing 30 feet of growth in one season • Each plant can produce over 100,000 seeds • Seed dispersal is by wind, water, people and other animals • Can also spread by fragmentation, when roots are produced from stem fragments, typically from older stems, which can hold more water.”
My experience with this Clematis has been discouraging. The reasons are twofold. First, few people seem to be aware of the severity of this invader and as a result established plants have been largely ignored resulting in a huge build up of a bank of seed on the ground locally. All you have to remember is that among the characteristics of an invasive plant is that its seed can remain viable for years until conditions are ripe for germination to realize how frustrating its control and eradication can be. Second, after several years of growth a single plant can produce so many stems that finding them all in an overgrown landscape can be difficult and the following year may find you facing a problem that looks as bad as the previous year’s. We may need the persistence and dedication of monks to deal with this one.
How do I get rid of them? I‘ve always found the best control program to be prevention. Think about it, if a mature plant can produce hundreds of thousands of seeds annually, and mature plants can live at least 40 years…a single plant can contribute millions of seeds. Eliminate the sources and you reduce the opportunity for invasion. Get your neighbors to deal with theirs, help them, and don’t let your own go to seed. Normally, minimizing bare and disturbed soil helps immensely with reducing one’s weed burden. This Clematis, however, as a highly successful invasive is particularly well adapted at insinuating itself in the most difficult to reach places, deep within the crown and foliage of some highly valued plant, and established native landscapes, where more common weeds have difficulty getting a start. Regular grooming of one’s beds is a necessity. Pull them out as soon as you find them and look often. This kind of monitoring will always remain necessary. While they will take a few years to flower and set seed, you don’t want to give the plant time to grow its root system, that will only make its eradication more difficult.
If you are unfortunate enough to have inherited someone else’s ‘legacy’ of Clematis vitalba, your task is daunting, but doable. Spraying vigorous vines and climbers is problematic. You can do this especially in cases where the vine has buried everything beneath it. Much damage can be done to the surrounding and supporting vegetation is still up struggling to compete. Spraying this must be done when in leaf as there is no leaf surface to takeup the herbicide when sprayed in winter, when many desirable plants are dormant. Attempting to disentangle any vine from supporting and desirable vegetation is practically impossible. I’ll spray where I can and elsewhere trace the ropy stems back to the root crown and grub it out when I can. Keep in mind that this plant can form a mat of stems a foot or more thick on the ground. In other cases I cut, rip and tear at the stems to the root crown or rooted nodes and immediately apply an herbicide like Lilly Miller’s Blackberry and Brush Killer (contains Trichlopyr) or Roundup (Glyphosate), using the concentration recommended for ‘stump treatment’ on the label. Again always remember that the label is Federal Law. It is necessary to apply it to fresh cuts because woody plants will quickly start to ‘wall off’, or compartmentalize, protecting healthy tissue which will also work to inhibit the uptake of the chemical…bad. A relatively small volume of chemical is used. This requires that you use a much higher concentration than for general spraying, but because your application is more accurately directed, there will be fewer potential deleterious effects on the environment. For those who are opposed to the use of chemicals in the landscape remember: if nothing is done we will loose the battle against invasive plants and with that loss countless native plant species and the fauna that have evolved with them and are dependent upon them, not to mention our prized ornamental gardens and landscapes. We have ‘broken’ our landscape and ignoring the problem or denying our responsibility will only assure greater loss C. vitalba can be weakened by persistently cutting them back hard, but it is very doubtful that such an effort will be continued both long and frequently enough to result in its death. Your only other choice is to clear your entire site, which does not assure you will have a weed free landscape later. We have collectively created this problem and it is now ours.
When battling one’s resident invasives, whatever course is chosen, vigilance will be required long after your decision is enjoined due to the longevity of the seed and the likelihood of re-infection from other sources. Nature and life never stop. There is no quick fix. No single horticultural silver bullet that once fired does away with our enemy permanently. We should always keep in mind Sun Tzu’s maxim from The Art of War, ‘Know thy enemy’, so that we are not defeated as a result of our own ignorance. If we don’t do this, if our efforts are misdirected or we simply tire of the task, our previous work will be wasted. There is much that is beyond our control so we must utilize the tools and knowledge available to us. These plants are realities in our lives. They are here, brought by us, or by our predecessors, and are now our responsibility.
Our gardens offer us little lessons in humility. They are collections of our sins of desire and of those who came to this piece of land before us. They accumulate, in a very real way adding to the memory of the land going back to its undisturbed state. Each plant cut and removed, each plant added with intention or by accident, has shaped our gardens as roots move soil and leaf cast shade. Graded by shovel or blade, soil has been laid bare, fences built and stone work laid, roof and gutter alternately drying or flooding each square of soil. Even our long dry summers have been broken with hose and watering can, nozzles and timers. Now, alongside our Stewartia and Daphne, Canna and Epimedium grow our own individual community of weeds, dynamic, on the move, always ready to incorporate a new member or take advantage of our neglect. Step out into the larger landscape, and the gardens of others, and we see the scale of our ignorance and arrogance. This larger ‘quilt’ of landscape, stitched together, separated, into yours and mine, leaves much land neglected and over run, threatening our own. Of all of the plants we have brought here there have been a relative few that have escaped and become serious threats. We remain the larger threat as we continue the pattern of disruption that seems integral to our way of being on the land today. If we look at the larger landscape as a part of our own gardens it can give us a perspective that we might otherwise miss and it can humble us in ways that will move our hands both more respectfully and effectively in our chosen home.
The following link will take you to the page, “Invasive Weeds in Forest Land: English Ivy Hedera helix”, and contains a lot of additional information from the Oregon Department of Agriculture. The ODA is responsible in Oregon for overseeing the application of pesticides, which includes herbicides. It issues licenses, revokes them and assesses penalties for violations of the law concerning their application. I suggest you read it, particularly the sections following the heading, “Recent Herbicide Research Conducted in Portland”.
The work begun by Sandy Diedrich in 1994 by the No Ivy League, continues under the auspices and with the support of the City of Portland Parks and Recreations. Their site contains much helpful and current information on techniques and events as well as other helpful links.
I frequently visit the CABI Invasive Species Compendium site for plants new to me. It includes plants suspected of being invasive anywhere in the world. Many won’t be in your particular region, Clematis vitalba is problematic here and in many other regions of the world. It looks closely at with those conditions supportive of it, its ecology, history, management practices and just about anything else you can imagine about the plant.