Will cardboard sheet mulch kill buttercups?

I have a fairly dense bunch of buttercups - about 3 feet in diameter. This was my first experience with these "pretty little plants" and I was unprepared for what a pest they can be.

I have cut them all the way down to the ground, shaving the soil, along with other plants, preparing to sheet mulch and create a raised bed where they were.

I uprooted the ones within a foot of what will be the edge of the raised bed.

Will several layers of corrugated cardboard, carefully applied (edges overlapping 6", etc.) as a mulch, with 6" of composted leaves on top of it, kill the buttercups?

Or are they like bindweed, and they will generate so much life force from the roots that they will grow tendrils and extend beyond the cardboard and continue to be a problem?

This time, however I know to pull them up as soon as I see them.

I am preparing to plant now, and they did produce seeds.

They appear to be shallow rooted, but appearances can be deceiving. Does anyone know the root structure?

I know that deep rooted plants like bindweed will only be slowed down by such a cardboard mulch.

I also know that buttercups are powerful little plants. They started in a dense stand of clover in the lawn, and there is now very little left of that clover, and lots of buttercups.

They are very smart about finding the moist places, sending long tendrils toward them. The bed will adjoin a spot where there is a large rhododendron with lots of violets underneath it - a moist place.

Please say, in your answer, if what you believe is based on experience or reading or theory.

I would like to put down the cardboard mulch tomorrow.

Thanks to all who can help.

Pamela Melcher

I live in Portland, Oregon, zone 7/8.

Pamela Melcher

how much cardboard are you talking and do you expect to ever remove the cardboard? cuzz the answer is unfortunately no. I have buttercups from 1 inch to 3 feet tall, cardboard doesn't stand a chance against the dormant rhizomes and generations of seed.
What does work but it's no instant gratification is solarizing the plants and soil with 1 summer under black plastic. Reveal in the fall to start germination of the seeds then cover for 1 winter, the next year you will have gotten ridden of 95% of it. Rodents will have a burrow fest under the waterlogged soil and in the spring you can create the type of garden or broad scale planting that's appropriate to your local conditions.

I had to get bees because I can't harvest enough of it for the ducks to make a dent in an acre, it makes good mulch or compost fodder if you can mow it down and collect it mechanically but it's not worth it by hand. What I've found more effective is to cardboard it; cut chunks of it out and replace with compost and plant with potatoes. I noticed one year there was an empty spot in the buttercup coverage and when I checked it, potatoes planted from years ago had regrown multiple times in the same spot. The organic matter potatoes leave behind displaces the rhizomes which only dominate in unfavorable conditions. Where I had black plastic I planted flax and potatoes bare soil and just walked away. In the next few weeks i'll start sowing peas and radishes into the die down, the key is not to harvest the potatoes but let them bulge the earth and then bring in the rodent highways that destroy the rhizome matte over the winter. They never get all the potatoes and the next year the potatoes return to build and dominate the soil. The radish and peas I want for there greens I leave as much roots in place as I can during a soil reconstitution phase. Buttercups really identify an oxygen problem in your soil, that plant doesn't drown.

Hi, Saybian,

Thanks - wow.

The patch of buttercups is only about 3 feet in diameter. I dug all the roots that were up to 1 foot from the edge of the patch. I dug down about 1". The roots seemed to peter out below 1". So the patch that has not had the roots dug out is now only about 1 foot in diameter. I can dig all the roots out down about 6 inches. Not fun, but doable. IF they are not deep rooted, that might do it. Do you know how deep the roots go? I guess I can dig down and see for myself, actually.

The cardboard could be quite thick. My plan was to let it stay there until it rots. A thick layer takes a LONG time to rot. At least 2 years. I have easy access to cardboard boxes. My plan was to put on top of the cardboard a 6 inch bed made from composted leaves - very high in organic matter.

And I can dig out all the roots in the soil below the cardboard.

There still are the seeds. But the tiny plants would be very easy to pull. We just have a 1/4 acre lot - nothing huge.

Do you mean buttercups indicate low oxygen in the soil?

There were only a few of them when we moved here 2 years ago. I had no idea what a pest buttercups are. I could have easily prevented this mess .

To summarize, if I dig down 6 inches in the 3 foot diameter circle and get all the roots there, and the cardboard is very thick, might it be possible that would work? It would not work if the roots are very deep.

Thanks.

Thank you for sharing your technique. It sounds interesting.

Pamela Melcher

What is if you never remove the cardboard and just make a bed on the top and leave that bed? Then even buttercups should rot.
I never tried it but have tons of buttercups too. Sheep do eat these though, but as grasses envolved together with sheep buttercups might have done the same.

Thank you, Paula.

I did not make it clear, but what you suggest is my plan - to put down a thick layer of corrugated cardboard, and put 6" of composted leaves on top, and leave it, hoping that the buttercups will die and decompose under the cardboard. I will not till the bed, so seeds would not be brought to the surface.

I was wondering if they would sprout under the cardboard and creep along to the edge of the cardboard and resume their troublemaking activities, as bindweed does.

The roots do not appear to be long like those of bindweed, so it seems to me that my plan would work.

I think I will dig out the roots in that 1 square foot just to be sure.

The roots are thin, not like the ropey roots of bindweed. And they are easily broken, unlike bindweed roots. This suggests to me that they would rot fairly quickly. I will post my results, although it will be a while before they are evident.

Thanks, all.

Pamela Melcher

Pamela, I live in NE Portland and am having the same buttercup problem (was also clueless about how pesky buttercups were until recently). I'm wondering whether your solution worked, or whether you might have other suggestions for me. Thank you!

Mindy Fitch

Hi, Mindy,

I talked with Dave Jacke, one of the leading permaculturists, about the buttercups that are in the garden, and he was very skeptical that just cardboard would kill the buttercups because the patch is about 6-8 feet in diameter. He advised putting clear plastic over the patch throughout a summer for the sun to bake them to death, or digging them out.

There was a much smaller patch (about 3 feet in diameter) where I dug out all the buttercups, and as the rains came most of them were still dead...only the ones that were still alive had about 3 inches of roots and a bunch of roots from the same plant left. (like about 10 roots) The ones at the edge of the patch are easy to get. Only the really big well established ones are difficult. But the problem roots only go down about 7 inches. The roots branch out into about 10 roots that are about 1/8 inch in diameter.....stubborn little critters. That place where I dug them up was sheet mulched with cardboard and compost and there has been no further sign of the buttercups there.

The problem is to follow the little tendrils at the edge as far as they go, which, if going towards a damp area can be about 2 feet.

I plan to dig out as much as I can of the 8 foot patch. They can be dug individually...I do not have to dig up every shovel full of the area. The small ones can be dug as I used, before I learned better, to dig dandelions - which I now encourage to go to seed and do whatever they want. We have a small space and I am not waiting a year. It is vastly easier to dig them when the soil is moist. The teeny ones at the edge are easy to uproot.

Sorry not to have a quick answer for you....I sure had no idea that buttercups were such a problem......yoicks. But at least I think I may be sparing you wasting time on solutions that do not work.

Good luck. I will send you light as I dig my buttercups.....there were so few at first...and they are pretty so I ignorantly let them be...I could have nipped this in the bud but did not know.....I just have to laugh.

If you find out some amazing simple solution, please let me know and I will do the same for you.

Oh, I just noticed that you only joined yesterday.....well, usually I learn things that save me a lot of time on these forums. It will probably be up hill from here....Best wishes.

Thank you, Pamela! I'm on the PPG list as well, and this began with a buttercup question someone besides me posted there. May I please quote your latest update in an email to the PPG community?

Sure. Spread the word to watch out for buttercups....lol...good luck.