Goutweed (Bishop’s Weed), One of the most Difficult Invasive Species to Control:
Time to Re-think Our Approach to Aegopodium podagraria
Prepared by Mike Bald of Got Weeds?, 2013
So as the question continues to pop up, at workshops, conferences, and seminars, I’m inspired to offer a few
thoughts related to managing goutweed. Over and over it re-surfaces….”what about goutweed?”, “how do I
get rid of goutweed?”, “what a nightmare, nothing works”, “it’s gone for a while, but then comes back even
stronger…”, “this plant is driving me insane!”
OK, point made. Yes, terribly challenging, and no, right up front I’ll say that I do not possess the clear,
absolute, tried-and-true solution to a goutweed infestation. But I’ll offer some observations on what I’ve
seen, and then make some suggestions that may serve some of us in some situations. How’s that for vague?
Invasive plants are relentless, tenacious, and persistent. They have to be, but the vegetative spreaders are a
difficult bunch to manage, and it’s likely that goutweed tops the difficulty list in that category. What’s more,
the non-native invaders are often generalists with few checks and balances impacting their spread or keeping
them contained. To clarify, my thoughts here are based entirely on what I’ve observed on New England
landscapes with the associated climate and land-use patterns.
Goutweed thrives in shade, all variations of shade: partial, full, and deep. I’m assured that it also manages in
sunlight, although this is where there have been major differences in its durability and viability. Goutweed in
full sun does fine if its feet are able to stay moist. Wet is even OK, but a close-cropped hayfield which gets
scorched by direct sun seems to hold up well against goutweed. At least that’s the deal in Vermont.
Compaction likely plays a role as well. Interestingly, more organic content serves to hold moisture better and
thus works to enable the spread of goutweed. The only place I have ever seen full sun hammer goutweed is
in a very dry situation, not necessarily sand, but definitely quick to drain and quick to heat up.
Landowner management efforts to control goutweed have relied heavily on smothering and excavating. Or a
little of both, and yes, people have tried chemical treatments, repeat cuttings, black plastic, and heavy
mulching. Sunlight management is traditionally a powerful tool in controlling the spread of plants, but not
necessarily with goutweed. In the end, none of the methods seems to work; in fact, goutweed often slides in
opportunistically on sites where other species are the primary target. One common mistake with the
vegetative propagators is failure to tackle the entire patch at once. Of course, it’s not unusual for the patch
to be irregular, uncooperative, difficult to outline, and only one of multiple non-natives on a complex site.
While mowed walking paths can be maintained through or adjacent to a goutweed patch, it is not possible
to eradicate a well-networked population in piecemeal fashion. My opinion.
So as the stories continue to pour in, the list of failed efforts grows to include ever more methods… grazing,
flaming, sifting the soil, removing the top layers entirely, repeat-cutting regimes, and countless other
approaches. Last summer however, I found myself admiring a nice daylily patch, and I commented to the
landscaper how nice it was to see something other than goutweed. At which point he advised me that the
defined, stone-bordered patch had once actually been goutweed. He thought nothing of that point and
made to continue on his way. I double-checked with him, just to be sure I’d heard correctly. Yes, over five
years, the goutweed had faded out and yielded to the lilies. The cool part is that this transition occurred with
SOME investment of maintenance energy and initial work, but not really all that much. The property itself
was in transition, and invasive species were not a terribly high priority. That said, the lilies looked great
occupying a space almost the size of a pick-up truck. And goutweed was in no short supply everywhere else
on the property.
Another observation: goutweed was often planted deliberately as a decorative edging for rock gardens or as
a surround for landscape trees. Lovely indeed with its variegated leaves, but the green-and-white plants
almost inevitably revert to the more aggressive, full green variety on some unseen cue. At that point we see
the weeds “escape cultivation.” Jump the stone wall, run along a drainage swale, or what not. But which
direction do they go? Sure it’s easier to move downhill or to be moved unintentionally by either small
animals or lawn equipment. But all things being equal, where will the escapees run to? I can say that I’ve
never seen goutweed bolt toward the sunny spot. I’ve seen it break out to the shaded side of a tree, but not
to the sunny side, at least not initially. And I’ve seen it hug the shaded ground beneath apple trees; the
sunny space between the trees remains grass, making for some very interesting patterns.
So I’ll leave it at that as far as specific observations. The occasionally successful eradication stories seem to
be perennially short-lived. Sometimes the return takes a couple years, but it does happen. So what do we
do here?
Back we go to the lily patch. What is it about the lilies that enabled them to outcompete goutweed? It just
so happened that I was also working to contain an infestation of black swallow-wort when I had the daylily
conversation. At the swallow-wort site, I took advantage of abundant hostas to fill in some empty space on a
stone terrace restoration. I noted that the hostas were a solid clump below ground; additionally, they
completely leaf over their immediate location. Nothing grows through the root mass of a hosta, and even if
that were possible, how would a plant find light under those leaves? A stray jewelweed is the only plant that
ever manages to pop through the hosta canopy. So after some thought I wondered whether a deliberate
planting of hostas, daylilies, and yes, even irises would bottle up rhizomal propagators like goutweed. Have
we been barking up the wrong tree trying to control goutweed above ground? What if we went below and
took up all the available space with super dense root masses? Couple that with lilies and hostas hogging all
the available light above ground and what kind of results would we see? Irises are perhaps not quite as leafy,
but they are surely the most dense below the surface.
So would it work to stop attacking goutweed at its center, its strength, and rather to come in from the edges
with a slowly tightening noose of dense alternative plants? Not all irises and lilies are native, and I certainly
would not put hostas in a forested setting, but for residential areas they seem to be a reasonable option. No
more smothering from above and then watching in horror as the patch expands laterally. The smother action
comes later, once the noose is in place. Now about this perimeter of dense material: I do not yet have the
perfect formula nailed down, but if I assess the site and the terrain, I can come up with a fitting recipe.
Perhaps I circle the target goutweed patch with first a ring of hostas and then a ring of irises. If I’m still not
comfortable with the odds at that point, I can then lay out a line of black plastic. Does that go toward the
goutweed? I think so, but that’s a theory requiring a little more field-trial validation. Careful documentation,
with a good set of before / during / after photos, should lead us to some reliable conclusions.
I’m thinking a couple growing seasons gets the perimeter situated, then it’s just a matter of herding the irises
and lilies and hostas toward the center, onto the goutweed. The beauty of this approach is that you really
only need to purchase plants once to get things started. Lilies, irises, and hostas sub-divide beautifully with a
little elbow grease, so you double your available material every couple years. Yes, a long-term commitment,
but so it goes. At least it has some chance of success, and long-term is how we should be managing in the
first place. Such an approach forces us to get involved, to manage actively, to maintain a stewarding
presence. There is no singular application of effort that trumps goutweed, or if such a method does exist it
has not been well-documented. So for all those residential landscapes that have fallen to goutweed, perhaps
the keyword moving forward is not eradication, but rather transformation or replacement or conversion.
Conversion to a new palette of more desirable, less intrusive and disruptive plants. It’s all in the approach,
and if we re-look our approach, we may discover those improved methods. I encourage everyone reading
this to consider below-ground containment in a new light. If it seems like a viable fit for your site, please
draw up a plan, start taking notes, and share what you learn.
Suggestions for Goutweed Control, the Abbreviated Version:
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Site specifics always play a role in determining treatment methods
Goutweed control should focus on long-term conversion of the site to less intrusive species.
Long-term refers to a five year program with emphasis on a constant stewarding presence. Five
years at minimum, constantly improving the site and reducing the goutweed population.
Avoid attacking goutweed initially at its center or its strength. Do the preparations first, around the
edges, before tackling the actual infestation.
Stressing a plant by cutting or smothering can force it to extend laterally: not the desired result.
The native / non-native issue is a consideration, particularly in woodlands or sensitive settings.
Bring the struggle to contain goutweed below ground; fill the space below the surface with dense
root clumps.
Shading must be at ground level as a sunlight intercept. Higher level canopy will not impair the
spread of goutweed.
Three plant species that eat up a lot of light at ground level and take up space below ground are
hostas, lilies, and irises.
First surround the target goutweed patch, on as many sides as possible. Construct a perimeter with
the hostas, lilies, and / or irises, and then work inward to smother or reduce goutweed.
The perimeter will consist of concentric belts, with an overall width determined by specifics of the
site. Black plastic could also fill a role as one belt in the perimeter noose.
Recall that machinery and even work boots can spread goutweed fragments
Propagate the desired plantings once they are established; they are a free and constant source.
Document the work in detail to demonstrate progress; share lessons learned.