tackling invasive plants strategically, with christian allyn

WHEN I SAW news of an upcoming webinar about invasive plants listed on the Pennsylvania Horticultural Society’s website, I knew I wanted to sign up and listen in. And also that I wanted to talk to the presenter, who founded a business in 2016 to help private and public land owners with the remediation of Japanese knotweed, multiflora rose, Oriental bittersweet, and other thugs that are crowding out native plants and destroying wildlife habitat.

Invasives are our topic today. Trigger warning: The subject of chemical use, and when it outweighs the damage done by invasives, is also part of the discussion.

My guest is Christian Allyn, who founded Invasive Plant Solutions when he was still pursuing a double major in horticulture and economics at the University of Connecticut. Rather than just watch the continuing ravaging of natural habitats (like the one in his photo above) by invasive species in Connecticut and Massachusetts, where he practices, he decided to do something, to make it his career path.

“This does not have to be our reality,” he says. “We can choose to restore nature.”

Plus: Christian is doing a virtual talk for the Pennsylvania Horticultural Society on solutions for invasive plants, at 5:30 P.M. Eastern time on February 22, 2022. I’m going to give away a couple of tickets for people to attend. Enter to win by commenting in the form near the bottom of the page.

Read along as you listen to the January 31, 2022 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

managing invasives, with christian allyn



Margaret Roach: Hello, Christian. I think we could all use a dose of your optimism and your determination and some of your how-to insights about dealing with invasives. And before we start, I want to say, for your online lecture for Pennsylvania Horticultural Society, it’s February 22 at 05:30 PM EST. I know I’m going to be attending. So, tell us just quickly about how did you get into this, and your background and what you do?

Christian Allyn: Yeah, certainly. So, it was a lifelong interest and it started on Easter Sunday, 1997, that was the firm start when I was all dolled up as a little Sunday school kid, looking off my parents’ porch in East Canaan. They built a house in an abandoned horse pasture, and the hedgerows were just atrocious, filled with invasives.

And on my father’s side, I am an old Yankee, and my grandfather, Paul Allen, who was a former first selectman here in North Canaan [Connecticut], often described playing with his friends in the woods. And same with my father. And I never had that opportunity. And looking into the hedgerows and into the woods and seeing the tangle of multiflora rose and bittersweet, I said to myself, this isn’t right, I got to do something about this.

So, that evolved in 2011, working with our locally famous Tom Zetterstrom and the Arboretum and Landscape Committee at the Housatonic Valley Regional High School here in Falls Village, planning and executing the removal of invasives from the north campus of the high school, which has been an ongoing process. But that served as the beginning of what could be built into a business.

Margaret: And so when you say, just for people who are elsewhere, you say East Canaan and Falls Village, we’re talking about Connecticut, the northwest part of Connecticut. But a lot of the plants we’re going to talk about today, sadly, are wide-ranging over large swaths of the country, not just here.

Christian: Certainly.

Margaret: So quickly, what’s an invasive? From your point of view, as someone who works to remediate, subdue, destroy [laughter], get rid of them, what’s an invasive? [Above, multiflora rose from Wikimedia.]

Christian: So invasive plants are actually defined by federal law. In 1996, President Clinton put an executive order defining an invasive plant as not just a noxious weed, but a noxious weed that is foreign to the North American continent and has the capability of reproducing and causing major economic or human-health harm. And part of that executive order, he established the ability for states to create invasive plant councils.

So here in Connecticut, we have a Connecticut Invasive Plant Council made up of scientists, professors, members of our ag extension service, DEP and other professionals in the field that catalog different plant species and rule whether or not they’re indeed an invasive plant.

In Connecticut, we have approximately 84 invasive plants. The list continues to grow as we discover additional species that fit that definition. There are aquatic invasive plants, there are terrestrial invasive plants. And my business particularly focuses on those terrestrial invasive plants.

Margaret: And so something can be a “weed” without being categorized officially as an invasive plant. So do invasives or do the plants that you tackle, do they have common characteristics that maybe inform you about managing them, is there something? Or do you look like, when you go to decide what the approach is, are there characteristics you’re … I mean, I’m a longtime gardener, so I’m weeding all the time, for decades, and I know the things that are rhizomatous are going to give me a harder time than certain other root systems and so on and so forth. So do you look for different characteristics?

Christian: Yes. So since 1996 when that executive order was passed, there’s been studies executed by our land-grant universities, including UConn, our ag extension services, not just in Connecticut but all across the country, as to the best management practices for each invasive plant. And especially whether or not you need to use herbicides or not.

So what I did, beginning at my time at UConn, was analyze the studies and fact sheets constructed by those services and decide, O.K., this is what Pennsylvania ag extension says is the best management practice. This is what the University of Connecticut says is the best management practice. And more often than not, those best management practices align.

And that type of system, it becomes very easy to execute once you understand that mode of action. So some invasive plants like multiflora rose, bittersweet, honeysuckle—once they’re in that hedgerow type of environment, a very similar management strategy can be undertaken. But if they’re on their own, a different management strategy would be undertaken.

And there are others that are invasive plants that are much more extreme, like Japanese knotweed which we could get into.

Margaret: Yeah, we will. And so you just hinted at the elephant in the living room with any conversation about invasives, is whether or not they can realistically be subdued/eradicated without chemicals.

And I have to say, even though I’m a longtime organic gardener, when I see the destruction of habitat that’s happening or has happened along the roadsides everywhere, the literal changing landscape—changed landscape. The lack of a forest flora, of a herbaceous layer, I mean, so much destruction. I start to wonder if saying no to chemicals 100 percent of the time is always feasible.

And even conservation organizations trying to reclaim important habitat and preserve land use them in the least-toxic way possible for the greater good to bring that land back to life and diversity.

So maybe you could explain the approach. Because you’re not out there all day long spraying thousand-foot long hedgerows with gallons of herbicide. That’s not the tactic.

Christian: No. It is the tactic occasionally. So, the situation is, we’re at a point where our land is corrupted by these invasive plants to the point where there is next to no habitat for our native plants, and in turn our native animals.

So what we have to do is remove the invasives at the right season, time of the year—and winter is the prime time for it actually, for the actual removal of the hedgerows in particular. And then thereafter only use the herbicide when necessary.

So some invasive plants like purple loosestrife, there was a biological control insect that was released in 2012 to specifically target purple loosestrife. So generally when I’m looking at a property and there’s a purple loosestrife problem, I generally do not advise chemical treatment.

However, with the hedgerow type of environment—with bittersweet, multiflora rose, honeysuckle—there are two different herbicides that provide the best management and least environmental impact. And they are both glyphosate and triclopyr products. So glyphosate and triclopyr are the active ingredients. And glyphosate, as you may know, is the main concern in the herbicide world right now, because it’s the active ingredient in Roundup.

So the key difference there is that glyphosate is the active ingredient, but the brand name, Roundup, or any herbicide brand name by law does not have to disclose to the consumer what surfactants or any other additive is in the herbicide that creates the result that it gives. So I only use Rodeo herbicide, which is a Dow Agrisciences, now Corteva Agriscience, product, which is wetlands-approved, and generally recommended by all of our extension services across the country for invasive management. [Photo of strangled tree, above, from Christian Allyn.]

Margaret: So, you really drill in to get to the right solution with the least impact—sort of the spirit of integrated pest management, even though these are plant pests rather than insect pests. I mean, to do the least harm while doing the greatest good.

Christian: Exactly.

Margaret: Each action.

Christian: It is truly a prescription for the land.

Margaret: So, you’ve mentioned hedgerows a few times, and so let’s just visualize, let’s paint a visual picture. So I’m driving along the road, even where I live, and it’s just changed in the last two decades especially. You mentioned multiflora rose and honeysuckles and bittersweet, and the privet, the miles of privet, barberry.

So a hedgerow is what it sounds like, it’s like a thicket so to speak of woody plants that have sort of tangled together, is that what you mean by hedgerow?

Christian: Well, there’s our native hedgerows and then there’s our corrupted invasive hedgerows. So, I guess the two examples for our area in northwest Connecticut that you could use is, if you were to drive in route 41 in Sharon, or route 22 in New York State, and you would look off into the farm fields and you would see these swirling masses of plants, just chaos. That is multiflora rose, honeysuckle, bittersweet and other invasive plants, all tangling around our native cherry trees, our dogwoods, our ash trees, which are all in the process of dying right now, as I’m sure you know, and our listeners know.

But if you take a drive, even north into Franklin County, Massachusetts, into Monroe, into Florida [Mass.], you will see our native hedgerows, which have beautiful sugar maples and cherries and dogwoods that are uncorrupted, that are clean, well-formed. And that’s what our area looked like not even 50 years ago.

Margaret: Correct.

Christian: And we can get it back to that scene, using the right strategy and with limited use of herbicide.

Margaret: And does that start with, at some particular time of year, when we’re talking about a woody—these are woody things—does that mean first cutting them down? What happens?

Christian: Yes. You have to remove what I call the biomass. It’s a really an invasive-plant biomass because it’s different species all tangled into one. So in that extreme invasive plant pressure environment, the best thing to do is to either brush hog or forestry mow the entire hedgerow. In that process, you will uncover the trees that were casualties of the invasive plants that should also either be removed or left as snag trees for-

Margaret: For wildlife. Sure.

Christian: Exactly. So that process should be executed in the winter, roughly beginning in November and ending in mud season, March or April.

Margaret: So we’re cleansing the palette in winter [laughter]?

Christian: Exactly. Burning off the deadwood without fire. So, the hedgerow is now clear. And in that process, sometimes you’ll find red twig dogwood and gray dogwood and viburnum that are in those hedgerows that you could either avoid cutting down, or unfortunately are within the path that they must be cut down. Regardless of whether they’re cut down or … Well, if they are cut down, they will re-sprout. So all of our native and invasive plants in that hedgerow environment will re-sprout in spring. So what a contractor like myself can do is take a ride along the hedgerow and spot-spray treat each invasive plant and avoid each native plant.

Margaret: And when we spot-spray, we’re not talking about, again, broadcasting like huge spray of … we’re talking about really targeting onto the stump or whatever’s left or the beginning of new growth?

Christian: The stump will re-sprout into clumps of new growth. And that new growth in one season will be approximately 6 inches to a foot high. So we’re spraying little basketball-sized re-sprouting invasive plants, thus limiting the amount of herbicide we’re using.

Margaret: Right. O.K. And a lot of those plants that you just talked about, I mean, like multiflora rose … You’re talking about Connecticut and I live adjacent to where you’re talking about. But I mean, multiflora rose, if you look at the range maps, I love the… I forget the name of the website, the University of Georgia has a website that shows the range maps of invasive species around the country.

And I mean, if you look at the range map for multiflora rose, I mean, it’s in most of the United States. Japanese knotweed, maybe two-thirds or three-quarters of the country, except some of the arid-zone Western states, I think. And these are plants that have proven that they are not going to behave anywhere, really.

Christian: Certainly. This type of hedgerow corruption exists as far west as Minnesota, into Canada, and definitely south into the Deep South of the United States. And a different form of it exists in Europe. There are North American plants that are invasive in Europe, and are causing very similar problems.

Margaret: Right. So speaking of Japanese knotweed, to me, visually, it’s been perhaps the most dramatic invasion I’ve seen in the last decade or two where we live—only because of its stature, and it actually has a showy appearance. You’re driving by and there’s this big stand of it and it catches your eye. It’s not indistinct by any means.

But this is a herbaceous plant, but it’s root system is, wow, formidable. So, how do you assess or figure out what to do with a beast like that? [Above, knotweed photo by W. Carter via Wikimedia.]

Christian: Well, it’s named knotweed for a reason [laughter]. And the reason why knotweed is such an issue is, exactly, the root system. So, in any plant, turgor pressure is the amount of water pressure a vascular system can take in and exert onto the soil or hardscape around it.

And Japanese knotweed is a clonal propagator, so anytime there’s a flooding event or someone simply just digs it up and puts it somewhere else, this knotweed will grow. Its roots will knot right up into our hardscape features, our stone walls, our foundations, our water lines, our power conduit, and destroy them. And that’s why it’s such an extreme concern.

I’ve been in buildings here in northwest Connecticut, actually across Connecticut, that have had knotweed growing through their foundations, that have had knotweed actually even growing through a building. I have a picture of a knotweed plant growing in the inside of a shed in Lakeville, Connecticut. So it’s an extreme plant.

And it is very herbicide-resistant, if you use the wrong formulation of herbicide. The only way to remove knotweed is either using a glyphosate product or an imazapyr product. Those are two different active ingredients. And imazapyr, I generally do not recommend because it translocates. Glyphosate, according to our federal government, does not translocate. So, in a knotweed situation, you really have to use that herbicide in order to gain effective control at the right time of the year.

Margaret: So, do you wait till it’s close to flowering and cut it down first and then paint what’s left, what’s the timing here?

Christian: There’s three options. One is you could cut down the plants in June. By June, the knotweed stalks, they grow like asparagus in May, and then by June, they’ll be about 3 feet high. You could cut them down in May, if you’re not near a water body, or transportation of the stalks is not likely. Because if one of those stalks, up to a quarter-inch in length, gets anywhere else, it will create a new knotweed infestation.

So then by August or September after flowering, the plant will be 3 feet high, and then you could spray treat it with glyphosate.

If it is in a sensitive site, you could either not cut it and spray it when it’s at the 6-foot height,  which is generally what I recommend because you get the maximum intake of herbicide to really begin the dieback of the root system, which is necessary in order to maintain control. Or if it’s a very small infestation, you could actually inject the stems with glyphosate concentrate. Only five milliliters per stem will kill each stem.

I’ve been at sites here across Connecticut where there’s maybe 15 or 25 stalks of knotweed in a very small infestation. And after injection in the second year, there’s next to no knotweed left.

Margaret: Right. And that’s a minuscule … it’s not not chemicals, but compared to spraying a massive infestation in full in its full glory up above ground, I mean, that would use a lot less I would imagine chemical?

Christian: Well, it’s interesting. Once you dilute Rodeo or glyphosate to the proper levels, you’re using very limited actual concentrate.

Margaret: I see.

Christian: So when you’re injecting, if you’re injecting a small site, you will be using more chemical than you would if you were spot spraying, but it is a very targeted control. And it’s very unlikely you will get any herbicide in a place that it does not belong.

Margaret: I see.

Christian: Unfortunately though with knotweed, we have infestations across the United States that are enormous. If you look at the Connecticut River and the Deerfield River up in Massachusetts, or the Delaware River, or any of our interstates and state highways, our larger state highways like Route 8 in Waterbury and Route 2 in Glastonbury, it is a knotweed clone. And that’s going to require some intense maintenance.

Margaret: I just want to ask about my particular obsession, which is Oriental bittersweet, a woody vine [above, uprooted showing its characteristic orange roots]. And the birds love to gather the fruits and then poop out the seeds all over the place. And I feel like what I do most of my gardening season is pull up bittersweet seedlings. Is there any hope for bittersweet? And is that one where we should cut down the big woody vines to the ground, paint the stump with a chemical? I mean, what about that?

Christian: Right, so that’s the best-case scenario. Is if you have a single or a forest stand where you could obviously see each bittersweet vine, you could cut them, treat them with Rodeo concentrate in a device known as a Buckthorn Blaster, which is just a modified bingo dauber with glyphosate and blue dye in it. That is the best-case scenario.

In those hedgerow type environments, it’s best to clear the bittersweet out and then either spot spray or treat the stump if you could find it.

But the key thing with bittersweet is it has a seed-latency period, meaning that the seeds are alive in the soil for up to 20 years. So you have to keep an eye out for those seedlings every year or else you could have the infestation grow right back. Other invasive plants have lower seed-latency periods.

Margaret: Yeah. The seed bank on that one is like, whoa, it’s unbelievable [above, just one handful of uprooted seedlings at Margaret’s]. And which I think is part of its big success, obviously, is that it has that going for it.

So you’re going to do this talk for Pennsylvania Horticultural Society, February 22 I think it is, in the afternoon.

Christian: That’s right.

Margaret: And what do you think the most popular plants that people, because there’s going to be a gardening audience, are going to ask you about? What do you think they’re going to be asking you about, English ivy [laughter]?

Christian: Well, certainly bittersweet. Some of the other shrub invasives, like honeysuckle or barberry, will come in. And barberry attracts ticks, so that’s another concern for people. But I think the two heavy hitters will be of course Japanese knotweed, but also goutweed, Aegopodium.

Margaret: Right. Of course, of course. Yes.

Christian: And Aegopodium requires chemical treatment, but it can be effectively either dug out if you are very-

Margaret: Diligent.

Christian: Diligent about it, and targeted, and also use the herbicides in tandem. But it takes years of followup in order to effectively gain control.

Margaret: Yeah. Rinse and repeat, rinse and repeat, rinse and repeat, it’s a lot of do-overs.

Christian: Right. 90 percent, 95 percent, 99 percent, and then you have that 99.9 percent until it’s truly gone.

Margaret: Well Christian Allyn of Invasive Plant Solutions, thank you so much for making time today. And I guess you’re going out to mow down or brush hog down a couple of hedgerows, right?

Christian: Well, actually what I do is I have forestry-mowing contractors, so if there’s any forestry-mowing contractor listening, I’m happy to work with them.

Margaret: [Laughter.] Yeah, I bet.

Christian: They do that. And I do what I’m good at. Sharing is caring [laughter].

more from christian allyn

enter to win a ticket to the invasive plant solutions webinar

I’LL BUY TICKETS for two lucky listeners to Christian Allyn’s February 22, 2022 webinar on invasive plants, for the Pennsylvania Horticultural Society. All you have to do to enter is answer this question in the comments box below:

What is the most troubling invasive where you live–or even in your garden?

No answer, or feeling shy? Just say something like “count me in,”and I will, but a reply is even better. I’ll pick two winners after entries close at midnight Tuesday, February 8, 2022. Good luck to all.

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the January 31, 2022 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

  1. Susan Plunkett says:

    Japanese knotweed is a horrible menace! My husband adores native plants (thanks, Native Plant Trust for your superb Certificate programs!), and the property we bought has a nasty knotweed problem He has tried to be targeted with pouring Roundup into the hollow stems of younger portions, but it keeps popping up in other areas nearby. The other product you suggest might be needed…

  2. Marianne Pollak says:

    This is so helpful….I have a major bitersweet problem…we have property that ends at a pond and we love the look of the “natural area” leading to the pond. BUT, we now realize with the passing of time, it is no longer as “natural” as we thought…working hard to conteract, and so much of what Christian Allyn and you discussed is so helpful.

  3. Sherry Greer says:

    My nightmare is Japanese stiltgrass. I try to hand-pull it, and fortunately it has shallow roots, but it spreads incredibly fast. Is there anything that will kill it (safely) without killing everything else around it?

  4. Sue says:

    And wild parsnip is challenging to remove with it’s potential to cause rashes when skin that has touched it is exposed to sunlight.

  5. Robert Sheridan says:

    The invasive plant presently of greatest concern to the residents of our park community is Japanese knotweed. On my lot I contend with multiflora rose and barberry.

  6. Kate Kasdorf says:

    The most troubling invasive here is bittersweet. We also have the rose and Japanese knotweed, but they aren’t as widespread. I have a hard time eliminating the rose because it is so pretty. But I do pull up seedlings that I see. Bittersweet is out of control on my 3 acres, and since I abut a large parcel of woodland, this will be an ongoing problem.

  7. Catherrine Salam says:

    I had the landscape pros come and removed a decades old Chinese Privet hedge last April. Still struggling with the Oriental BIttersweet that was entwined with it.

  8. brenda rumfola says:

    I have a lot of invasives on my property, and it’s a toss up as to the most annoying being multiflora rose and autumn olive.

  9. mary d pierce says:

    Just an FYI, poison ivy is a native plant. Although most people are allergic to it, it is an important food source for birds. Unfortunately, it often grows with English Ivy, so contact can’t be avoided. There are products that can be applied to the skin before and after gardening which help prevent rash.

  10. Katherine says:

    I’m trying to keep my landscape native in Northern Idaho. We live on two acres. I appreciate and respect my natural habitat that brings joy, not only to me, but deer, bees, hummingbirds, bats, etc. I want them to feel right at home, because it is their home! Unfortunately, some unwanted vegetation comes in and it sure would be helpful to attend the invasive plant webinar. The webinar would be invaluable to make sound decisions and keep a good balance for my little chunk of earth and all creatures great and small. Thank you for the podcast.

  11. Jeff Bell says:

    My problem is goutweed. I inadvertently spread it around in my early naive days of gardening. It is now present in several areas of my property. I spend many days every season hand digging it. I would so love to eradicate it for good!

  12. Dianne Plantamura says:

    I manage a small native plant garden on 50 acres of neglected town conservation land. We have bittersweet and multiflora rose everywhere and we need a plan!
    I’d love to hear Christian Allyn.

  13. geri friedman says:

    What Christian says about using herbicides is exactly what I learned in the master gardeners course I took with Purdue Extension years ago. I’m glad to have that corroborated and to learn about a gly[hosate product that is not Roundup.

  14. Kobi Carpenter says:

    We have blackberry vines that take over everything. We have tried for years to get rid of these vines but can’t seem to.

  15. margaret says:

    AND THE WINNERS ARE: Douglas Proops and Rebecca Wunderlich. Thanks to all of you for participating, and sharing your invasive plant stories.

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