Soil Rehabilitation

Sheet Mulching over Aggressive Perennials


Trumpet vine (Campsis radicans)

We permaculturalists like to say there is no such thing as a weed, just a plant whose virtues we haven’t yet learned to appreciate. But when we talk about sheet mulching, we’re usually not concerned just with improving the soil, we also intend to smother the existing, unwanted vegetation so we can start fresh. In fact, I will bet you that every single time you hear someone say a sheet mulch "didn’t work",  what they mean is that it failed to kill the weeds. Let’s call a spade a spade: if you’re sheet mulching, you want the weeds to die, and if it doesn’t work the first time, you want to know why not.

In any given climate, some plants will be more difficult to smother than others. For example, some posters to permaculture forums have tried and failed repeatedly to smother Bermuda grass (Cynadon dactylon) and bindweed (Convolvulaceae), while I’ve had little trouble sheet mulching over these at any time of year in my own climate. I’ve now discovered one plant that requires special treatment in my climate — trumpet vine (Campsis radicans) — and I’d like to share my experience in attempting to eliminate it from my garden.

First, a little about the location. I’m in eastern Kansas, in the central United States, just east of the Great Plains. The soil is extremely heavy clay, high in nutrients but difficult to work and counterproductive to till unless it is very dry. The summers are variable; when they are mild (27°C/81°F) both wild and domesticated plants grow vigorously nonstop from June until September, but when a summer is hot (40°C/104°F) and dry, the year effectively has two growing seasons with a lull of 6-8 weeks when the only creatures growing are grasshoppers.

Having converted my own property (by sheet mulching, never tilling) to mostly perennial food plants, I turned to an elderly neighbor’s spectacularly overgrown back yard to grow annual cash-crops for market. She agreed to let me garden there in exchange for taming the vegetation and giving her some of each year’s tomato crop. Her lot featured an overstory of giant ragweed (Ambrosia trifida), but once I removed that for use as green matter in another sheet mulch project, I found a densely tangled undergrowth of unwanted and unpleasant plants, dominated by trumpet vine.


View from alley before weeds were cleared



View inside the fence before clearing weeds

Trumpet vine is native to this part of the world, and cultivars are sold openly as decorative plants. A neighbor across the alley from the property in question probably planted it on purpose at some time in the past. Unfortunately in the damaged habitat of a backyard garden it spreads aggressively both above and below ground and is very difficult to get rid of due to its large (up to 7 cm thick) woody roots. I have broken a fiberglass shovel handle trying to uproot the stuff. While conducting home inspections I have found vines entering an attic via the eave soffit and twining through the darkness for several meters before springing out through a roof vent; I’ve also found it entering a basement through a crack half a meter below grade. Mowing it slows it down, but the coppiced stems that result grow thicker and tougher until they can stop a mower blade. Needless to say, domesticated garden plants cannot compete with it, and aside from possibly feeding it to goats, I do not think it has a positive role to play anywhere closer than Zone 5.

Since I hadn’t had to battle trumpet vine on my own property, I was curious to see what a simple sheet mulch could accomplish against such an adversary. I began clearing the neighbor’s yard in late August of 2012, laying down thick cardboard (over 1 cm thick) and reusing the weeds as green matter as I went. Once the weeds had wilted, I added a sprinkling of compost and a thick layer of dead leaves, then thoroughly watered the whole thing.


Vegetation removed from the nearest corner

First batch of green matter



The front line advances: note the earlier batch has wilted



The mulch gets deeper as the clear-cut gets wider

By spring (2013) the mulch had decomposed enough for planting, and I had a productive season, but the trumpet vine kept coming back from the roots. Every few days I had to pull it up, trim it back or dig it up — whatever I could do without disturbing the crops. I’m ashamed to say I tried agricultural vinegar and even Roundup on the blasted stuff, to no lasting effect! Meanwhile, a regimen of regular mowing supplemented by periodically digging out vine roots allowed the grass to reclaim the adjacent lawn so that I no longer had to defend the edges of the garden from 3-meter-long encroaching vines.

By June of this year (2014) I was ready to expand the garden and reduce the lawn, and I had an abundance of dead wood available, so I decided to try a layer of wood beneath the usual green and brown matter of my next sheet mulch. With a couple of friends’ help, we doubled the size of the garden in a few hours, first taking care to dig up all the trumpet vine we could in the area, then laying down thick cardboard, about 10cm of wood, compost, another 10cm of wilted weeds, and a top dressing of dead leaves.

In retrospect, my mistake was not waiting for the vines to go dormant. This being a mild summer, the vines grew up through the cardboard during July and August, twining themselves through the layer of wood until it became clear I would have to take it all apart and start over. This proved to be very labor-intensive.


Rebuilt woody bed at left; first attempt overgrown with vines at right;
previous year’s ordinary sheet-mulched garden in background



Rebuilt bed at left, woody layer at center, overgrown bed at right;
previous year’s sheet-mulched garden in background

When I took the woody beds apart, I was surprised to find that almost half of the wood I remembered putting in there less than three months earlier had already decomposed, along with all the green matter. I was pleased to find no evidence of termite activity — termites are a major concern here, and I’ve hesitated to implement hügelkultur for that reason.

It remains to be seen how effective this second attempt will be at discouraging the vines, but the main lesson I’ve learned is that attempting to smother them while they are not dormant is an exercise in futility. This is a change from my previous advice, to sheet mulch when green matter is abundant and ideally before it goes to flower, let alone to seed. That approach works well on less persistent weeds, but for woody perennials such as trumpet vine, timing appears to be everything!

Do you have experience fighting an aggressive perennial in your garden? I’d love to hear what worked for you!

19 Comments

  1. I have goldenrod and yarrow, which I use for compost. So I don’t want to get rid of it entirely! Otherwise, I have used this same method successfully!

  2. You want to remove the above ground biomass when the plant is actively growing, and remove that biomass to then starve the root system. Doing the same when dormant means the energy is still stored in the roots so the plant will have more energy to put into regrowth. It might take a few times,but you should be able to weaken the plant enough to mulch over it. You also have to consider that you have a root system that is potentially also fed rhizomatically from across the fence there so i’d consider digging a small trench to cut the roots off from potential parent plants.

  3. Our most tenacious vine here in Northwest Florida is Virginia creeper, although smilax is a close second. I haven’t had to deal with trumpet creeper yet, which we do have in this area, but I suspect it’s similar to Virginia creeper as far as eliminating it goes.

    I’ve had to clear some large areas dominated by azaleas through which these vines have been entangled. My strategy has been to cut everything to ground level using a reciprocating saw with a pruning blade (very fast and effective). I’ve then triple cardboarded, and then covered the entire area with thick leaves or wood chips.

    The vines outlast everything else, but I find that if I keep after them in terms of pulling or clipping fresh shoots, they eventually give up. It can take some time, though. I’ve been working on an area of serious Virginia creeper now for about two years. I keep clipping, though, and I can see that I’ll probably win the battle in the next few months.

    When I use cardboard, I’m definitely trying to kill the “weeds”. I understand that everything is a potential useful element, and “weeds” certainly fall into this category. But everything has it’s useful place. Very few of us would put chickens in the living room!

  4. Such an important issue. Sepp Holzer says of blackberry eradication, use pigs or you will need to work like pigs. Is a pig tractor or a chook tractor, or a tethered goat an option? I have tried placing corrugated iron sheeting over the sheet mulch structure, but it needs to be left for a very long time to work….

  5. We had a feral banana passion fruit vine that grew through everything! We ended up exposing the root growth and painting it with a mixture of 1litre of vinegar with 2 cup of salt dissolved in it. We don’t recommend using this unless you have tried all else but it will kill whatever it touches.

  6. I have over two Ha of organic apricot orchards slowly being smothered by grasses. I read elsewhere that in the USA there is an organic weed-killer which uses d-limonene (orange oil) as active ingredient. I’d like to try this here (in South Africa) but finding an organic-friendly surfactant is the hurdle – again, there are companies in the USA which make these (Mulse) but the cost of shipping makes this a non-option. Has anyone here tried to mix a home-made organic weed-killer?

  7. All plants die if you do not allow them to grow leaves, even large weed trees like camphor laurel I have successfully killed in 2 years and their roots just become compost corridors in the soil. You do have to cut all leaves and re-growth shoots while abusing the stump or stem every few weeks and it works every time, as no plants or trees can survive without photosynthesis.
    With a sharp edged tool we are in control if we love being on the ground in an intimate relationship with our system.

  8. Here in western NC (zone 7B) we have unsuccessfully tried to smother Bermuda grass with cardboard, manure, and lots of wood chips. We battled it for a while. Bermuda is in seed now so I may try some biodynamic techniques. But it clearly overwhelmed the berry garden. We’re re-locating any surviving berry bushes and turning the berry garden into a pig pen next spring.

  9. Hi Ben. Nice work! As to termites, it is worth observing to see whether they like humus enriched soil. At the farm here Down Under, ants are only prevalent where there is little to no top soil. The thinking here is that ants are the worms of the drylands.

  10. Our project this year has been expanding the garden over bermudagrass lawn by sheet mulching. First we place a 5’x10′ A-fram chicken tractor over the area for 3 or 4 weeks and let our six girls do their thing. Then we move the chickens to the next spot, soak the old spot with a hose. Next comes a deep layer of chop & drop – whatever is in season, then a layer of cardboard, then about 8″ of wood chips. Sometimes I’l throw some steer manure under the wood chips. Sometimes I’ll mix sawduat spawn (mushrooms) into the wood chips. After several weeks the bermudagrass starts poking through, but a gentle tug is all it takes to pull out the whole rhizome.

  11. Two things i learned in sheet mulching.
    Dead leaves as first layer – they are great at smothering.
    Cardboard as last layer – it breaks down much slower and does it’s job much longer.

  12. We’re developing an agroforestry property in Sth Gippsland. Good rainfall and fertile soil. Most of the property is currently grazing with good pasture on the creek flats and poorer grass on the steep slopes. We’re primarily planting trees on the slopes but with some in the better pasture. There’s a nice thick sward across most of where we’re planting. The conventional forestry approach to reducing competition from the sward while the trees are young is to spot-spray some roundup or other herbicide. We’d prefer not to use herbicides although its not out of the question. We could mulch but to provide mulch for thousands of trees effectively and cheaply is a bit of a challenge. We have loads of capeweed on areas the cattle have disturbed and, of course, grass that could be cut for a green much over newspaper or cardboard. Has anyone tried this on a larger scale? I’m curious if the cardboard/newspaper stays where it’s supposed to be on windy sites with a good load on top of it or if it ends up getting blown around.

  13. Here (southern South Africa) the Big Enemy is Kikuyu Grass. It sounds like your trumpet vine is almost as tenacious and aggresive as Kikuyu. ;) Over decades I have tried everything: like you, even Roundup and plastic sheeting, and the only truly effective strategy is to shade it out. Mulch is not, however, the optimal shading, since it merely provides an rich growth medium for the Kikuyu. (I have found Kikuyu runners growing over a metre deep, and it survives even extended distances and times underground.) I have sheet-mulched areas under mulch almost a metre thick, and all that happens is I end up with a metre-thick infestation of Kikuyu Grass.

    Shade from trees works (but comes with its own set of limitations and consequences.) Recently I discovered an indigenous flowering bush (to 2m tall) that self-seeds freely, yet is quite easy to remove by hand once it has fought back the Kikuyu. It is gaining a good foothold on land I want to get more productive, and is quite effective at outcompeting the Kikuyu. Then it becomes a harvest, and shred easily to make a fine mulch in its own right.

  14. This post is fantastic. Heavy sheet mulching is certainly not enough by itself for some plants in certain areas. I have Mexican Petunia (Ruellia) here in Central Florida which is the most invasive and also Bidens/Spanish Needle. The Bidens replicate by seed which is easy to take care of: Just cut them down before they seed and at least next year’s crop will be severely curtailed. Since they are also a wild edible, highly nutritious, that helps a lot in their use. Plants that grow from underground spreading rhizomes can be a major nuisance for sure. I have been able to keep the Mexican Petunia in check somewhat by cutting it down and hand pulling younger shoots out by the roots. There is always some left, not able to completely eradicate it yet. And, this year, when spring came, I got behind and barely did anything and it spread more than ever, expanding it’s borders about 2 feet over the summer. I will have to spend twice as much time and labor to now get back to where I was a year ago. I am hoping that by cutting it down in the winter, constantly pulling in the spring, not allowing it to flower (my variety spreads by seed, too!) will eventually have it eradicated from our property. There are some newer varieties that have been developed that do not spread so tenaciously but after my experience I would not want to take a chance that it was the right one as they visually look the same: a beautiful ornamental. Areas with much more freezes would probably not have this aggressive spreading.

  15. Please don’t buy roundup.
    Sending money to Monsanto is about the worst thing for agriculture one can do.

    Sometimes you just have to dig and fork for a time.

  16. Original poster here, following up a few years later! Last fall I told my neighbor that I would not be maintaining her yard for her anymore, because her grandson’s dog was very destructive to the garden, and it wasn’t worth my time to keep the dog out of the garden if they weren’t going to do their part. The grandson expressed some interest in gardening himself, and I offered to help him with it, and to help him keep the yard in check, but he didn’t, and the yard is nearly as overgrown now as it was when I started this whole thing 5 years ago.

    I’m pleased to report, however, that the lasting legacy of my tenancy on the land is that now when it gets overgrown, instead of trumpet vine and ragweed and sticky weed, it’s overgrown with sunchokes, comfrey, chives, and tansy! Much nicer, in my opinion.

  17. Hello!

    Thanks to this post I didn’t give up and resort to harmful (probably useless chemicals)! I have also had luck with (mostly) eradicating trumpet vine. I cut it to the ground and then smothered it with thick black plastic and carpet during the growing season then removed the masive roots and then covered with cardboard. This was last year and now that the growing system has begun again a few new sickly sprouts (white and red) have popped up but are easily removed. Plan to sheet mulch now and that should be the last of it.

Leave a Reply

Your email address will not be published. Required fields are marked *

Related Articles

Back to top button