Controlling and getting rid of houttuynia cordata - Ask Extension
Good Morning,
I just bought a house in Greenbelt and have a patch of what I believe is houttuynia cordata that I can't seem to get under control. ...
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Controlling and getting rid of houttuynia cordata #794458
Asked June 06, 2022, 11:52 AM EDT
Good Morning,
I just bought a house in Greenbelt and have a patch of what I believe is houttuynia cordata that I can't seem to get under control. Initially we tried cutting it back before we knew what it was (it hadn't flowered yet) but that just seemed to make it worse, and now it has taken over the whole garden. Unfortunately I think it has spread throughout the yard as well, though its hard to say for sure due to regular mowing. This plant really seems to enjoy the damp clay soil in our yard, which has abundant shade in the back but gets a fair amount of sun in the side garden where the largest growth is shown.
From what I can tell it was introduced here by a neighbor who had a friend gift it to her as "ground cover", and spread quickly in our yard which was largely neglected by the previous owner. Part of my concern is due to the location of our home, which backs up to Indian Creek and is very close to protected forest land; Greenbelt Park and the Agricultural Research Service are also in close proximity. We have been working our way into the garden pulling it out, but aren't sure how long it has been here/how extensive the root system may be.
Assuming our identification is correct, all the information I have found so far has indicated that it can be quite difficult to get rid of this plant so I wanted to reach out early for any guidance on the best course of action. While I know it isn't currently considered invasive, I was also wondering if there is anywhere I should report the infestation as the Global Invasive Species Database indicates cause for concern to native habitats, stating that "While the plant has apparently not escaped confinement, there is much fear that it will eventually present a huge risk to native habitats. It has a high reproductive and vegetative growth rate and quickly overtakes the gardens where it is planted. Control of this species is difficult as it will reproduce rhizomatically from fragments."
Photos are included below and any guidance you can provide is greatly appreciated.
Thanks!
Ashley
Prince George's County Maryland
Expert Response
Hello Ashley,
We agree this looks like Houttuynia, unfortunately. Eradication will be a tedious and possibly multi-year process because it's such a tenacious perennial. The use of systemic herbicide is the most effective and efficient approach, and you may need to add a surfactant (if the product allows and doesn't already contain one) in order to get the spray to adhere well to the waxy leaves of the weed. Glyphosate is one of the most commonly-used active ingredients in formulations of systemic herbicide. What doesn't enter the plant binds to the soil and becomes largely inactivated and immobile. Surfactants are sold separately alongside herbicides and other pesticides at garden centers since they are commonly used together. The label directions on the products will instruct you how to use them. Even with this tactic, multiple applications will be needed.
If you opt to avoid herbicides, the only practical option is to strip the soil with the rhizomes in it (we don't know how far down they'll grow, but guess it's in the top six inches) and bring it to your local landfill. This probably won't be a foolproof one-time solution, so expect to deal with some regrowth from any pieces that were missed. Composting won't reliably kill the pieces in the removed soil, though industrial-scale hot-composting might; you'd have to ask the landfill what they suggest or accept in each waste stream.
Smothering the weeds instead by depriving them of light might work, but will also kill any other plant growing among the Houttuynia patch (if there are any), and it could take over a year; to be fair, so would a non-selective systemic herbicide. The creeping vigor of this plant risks that they will creep outside of the light-blocking cover during this process, which would allow portions of the colony to survive since the photosynthesis will refuel the roots.
As it is, if any has grown under the neighbor's fence, it may persist and return in a future year, so you could ask them if they have it in their yard and if they are willing to control it at the same time. Alternatively, you could edge the fenceline with garden edging material to help keep it from creeping back in; bury several inches and keep a couple of inches above-grade so you can spot any rhizomes creeping over the barrier, as is done with containing running bamboo, though on a smaller scale in this case.
Even though this plant is highly aggressive and vigorous in home landscapes, interestingly (so far), it has not been found to have spread much into natural areas. Perhaps local conditions are not suitable for seed germination, or the plant doesn't produce much viable seed here for some reason. Maryland Biodiversity Project, a non-profit which documents the occurrence of all organisms in the state, does not have records for Houttuynia in wild areas. Mid-Atlantic Invaders Tool does, but in fairly scattered locations considering how popular the plant has been in years past in the nursery trade. You could try using iNaturalist to document/report the occurrence; they should have an option to distinguish the sighting as a cultivated/garden circumstance as opposed to naturally-occurring on undeveloped/unmanaged land, so any researchers using data can tell when a species is spreading on its own. You could also inquire with the MD Dept. of Ag., such as via the invasive plants program manager, to ask if the plant can be regulated (prohibited for sale) the way a handful of other invasive species have. The MDA is probably prioritizing regulation on species which are up-and-coming invasives, rather than long-grown species, but we do not know what their exact criteria are.
Miri
We agree this looks like Houttuynia, unfortunately. Eradication will be a tedious and possibly multi-year process because it's such a tenacious perennial. The use of systemic herbicide is the most effective and efficient approach, and you may need to add a surfactant (if the product allows and doesn't already contain one) in order to get the spray to adhere well to the waxy leaves of the weed. Glyphosate is one of the most commonly-used active ingredients in formulations of systemic herbicide. What doesn't enter the plant binds to the soil and becomes largely inactivated and immobile. Surfactants are sold separately alongside herbicides and other pesticides at garden centers since they are commonly used together. The label directions on the products will instruct you how to use them. Even with this tactic, multiple applications will be needed.
If you opt to avoid herbicides, the only practical option is to strip the soil with the rhizomes in it (we don't know how far down they'll grow, but guess it's in the top six inches) and bring it to your local landfill. This probably won't be a foolproof one-time solution, so expect to deal with some regrowth from any pieces that were missed. Composting won't reliably kill the pieces in the removed soil, though industrial-scale hot-composting might; you'd have to ask the landfill what they suggest or accept in each waste stream.
Smothering the weeds instead by depriving them of light might work, but will also kill any other plant growing among the Houttuynia patch (if there are any), and it could take over a year; to be fair, so would a non-selective systemic herbicide. The creeping vigor of this plant risks that they will creep outside of the light-blocking cover during this process, which would allow portions of the colony to survive since the photosynthesis will refuel the roots.
As it is, if any has grown under the neighbor's fence, it may persist and return in a future year, so you could ask them if they have it in their yard and if they are willing to control it at the same time. Alternatively, you could edge the fenceline with garden edging material to help keep it from creeping back in; bury several inches and keep a couple of inches above-grade so you can spot any rhizomes creeping over the barrier, as is done with containing running bamboo, though on a smaller scale in this case.
Even though this plant is highly aggressive and vigorous in home landscapes, interestingly (so far), it has not been found to have spread much into natural areas. Perhaps local conditions are not suitable for seed germination, or the plant doesn't produce much viable seed here for some reason. Maryland Biodiversity Project, a non-profit which documents the occurrence of all organisms in the state, does not have records for Houttuynia in wild areas. Mid-Atlantic Invaders Tool does, but in fairly scattered locations considering how popular the plant has been in years past in the nursery trade. You could try using iNaturalist to document/report the occurrence; they should have an option to distinguish the sighting as a cultivated/garden circumstance as opposed to naturally-occurring on undeveloped/unmanaged land, so any researchers using data can tell when a species is spreading on its own. You could also inquire with the MD Dept. of Ag., such as via the invasive plants program manager, to ask if the plant can be regulated (prohibited for sale) the way a handful of other invasive species have. The MDA is probably prioritizing regulation on species which are up-and-coming invasives, rather than long-grown species, but we do not know what their exact criteria are.
Miri
