Permaculture – more concerns

One of the gardening topics I’ve researched extensively is the use of landscape mulches.  (You can read a literature review I did a few years ago here.)  So I was more than a little frustrated to see one of the worst mulching techniques – sheet mulching – extolled in the book Gaia’s Garden (pp. 85-90).

Sheet mulches, like newspaper and cardboard, can be used successfully as a temporary weed control measure (i.e. a few weeks before planting a vegetable garden).  Long term, they are not a sustainable choice and often cause more damage to the system than the presence of weeds.

The two-dimensional structure of sheet mulches functions as a barrier to not only weeds but to the movement of air and water as well.  While this may initially increase soil water retention since evaporation is reduced, over the long term they will create soils that are unnaturally dry.  This condition is worsened on low-maintenance sites,where neglected sheet mulches easily dry out, causing rainfall or irrigation water to sheet away rather than percolate through.

In contrast, wet, poorly drained soils will become even more so as layers of moist paper or cardboard restrict evaporation and aeration.  Moreover, this condition encourages root growth on top of the sheet mulch, which can injure desirable plants when and if the sheet mulch is removed.

There are other disadvantages as well.  Exposed newspaper and cardboard mulches are easily dislodged by the wind, animals and pedestrians and often provide food for termites and shelter for rodents such as voles.  Combined with a somewhat marginal ability to control weeds compared to other organic mulches, sheet mulches are arguably one of the least attractive or effective choices for a sustainable landscape.

Sheet mulching proponents will argue that newspaper and cardboard are only part of the mulch structure – that organic materials such as compost and wood chips need to be added as well.  To which I respond – then why bother with the sheet mulch?  Why not just use deep layers of coarse organic materials?  That’s exactly what forest duff layers consist of.  It’s been repeatedly demonstrated that thick layers of coarse organic materials are the best and most natural choices for mulching.  (See, for instance, my  Ecological Restoration article on using a foot of arborist wood chips to suppress blackberry and enhance native plantings. )

The appeal of sheet mulching is its formulaic structure and logical approach – it’s like making lasagna (the name of yet another nonscientific approach to mulching).  Unfortunately, sheet mulching is neither natural nor particularly effective.

24 thoughts on “Permaculture – more concerns”

  1. I totally agree with you about this and I’m looking forward to reading the paper you provided a link to so I can give some of my clients something to chew on. Today I had a “last straw” moment in a garden I have been maintaining for close to 10 years. The client really, really has a hard time with leaves or any other material left on the soil and so I am always weeding unnecessarily and there are always moisture mainte
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    nance problems, among many other related issues. Though we’ve only had a 5 day stretch of dry weather here in south coast BC the surface of the soil is already grey, crusty and dusty and I know it will become hydrophobic any day now. Though I don’t claw at the soil to remove the weeds and instead slice under their crowns and leave what I can where it won’t be noticed or regrow it is still too much regular soil disturbance for my liking. And I – and the soil itself – cannot continue to tolerate soil surface conditions in May that are more typical of July. (Plus she has to stop standing all over her garden, but that is another issue!) So tomorrow I am taking a radical step and while the client is away in England I am going to mulch with the beautiful arborist chip that has sat unused in a heap (before I knew what GOLD it was) and hope that she sees the light. I am also applying the “it’s easier to ask for forgiveness than permission” strategy on this one, which I’ve learned is more often than not the best way to deal with fussy, reluctant clients. Plus I KNOW already that this mulch looks way better than grey, dusty soil.

    I will also relate my own sheet mulching story: many years ago I spent a considerable amount of time and energy laying down thick layers of newspaper and cardboard and then wood shavings over “lawn” (mostly plants other than grass) to make paths between raised beds. It seemed to work OK for the first season. But what happened was that I just created the perfect conditions for one of the WORST and most commonly persistent
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    (and foreign) weeds I regularly deal with which is Rumex acetosella, aka sour weed or sheep sorrel. This evil runner – though not as bad as Canada Thistle – quickly found its way between the newspaper/cardboard and wood shavings and spend a season furtively running amok in every direction only to pop up next spring beautiful and healthy and totally ESTABLISHED and in the raised beds themselves, saying “thank you for temporarily suppressing my competitors so I could really go to town!” I was so discouraged I actually abandoned the area for a number of years. Now the competitors have returned and the Rumex has diminished but I’m back to “lawn”. I now take care of it with my $500 string trimmer/brush cutter, which I’m glad I have but wish I had known that I should have instead put my $500 toward a chipper/shredder.

  2. Great post, Linda, and a really helpful comment, too, Natasha! I recently read about layering mulches, using wet newspaper as a base, and have wondered how it worked in the long term. I was going to give it a shot in one bed near the mailbox, and realize now what a big mistake that would be. Removing those aggressive perennials by hand may take more time and effort, but it sounds as if that’s the better course of action.

  3. Linda, based on my experience with the technique, I have to disagree strenuously with your assessment of the value and appropriateness of sheetmulching.

    I have used it in several sites very successfully for weed suppression and soil improvement. Granted, these were all in northern California, on similar (clay) soils, so the technique may not be universally applicable (but what is?).

    I have found that the sheet layer provides very effective suppression of annual weeds, where the seedling can’t force it’s way through the cardboard in the first year or two, and rots in place. Properly applied, it can even suppress persistent perennial pests like oxalis and bermuda grass. That’s a multi-year battle involving a couple rounds of mulching, but it does work.

    You describe a number of shortcomings, most of which can be attributed to using too little mulch over the sheet (a mistake I have made). Or ever trying to remove the mulch. (why?)

    Part of the point of sheetmulch is that it becomes part of the soil (so, like any natural mulch, it has to be renewed). Unlike the plastic mulches (which fail in a few years anyway) you never have to remove it — in 2-3 years, there’s nothing to remove. Sheetmulching isn’t any more “natural” than anything else humans do, but in this way it follows the fundamental permaculture principle of working with rather than against nature.

  4. Deb,

    My experience with sheetmulches has been that they are an effective way to control perennial weeds.

    Though I would not recommend using newspapers except to go around obstructions like existing plants. Cardboard in my experience is much more effective.

    You want to make sure that you overlap the edges of your material well, and avoid gaps. If you are covering a big area, get big sheets of cardboard. Appliance boxes work well, as do the boxes used to ship bicycles. (Take out the staples first.)

    My wife wrote up a guide to sheetmulching. I’ll ask her to post a link.

    What kind of weeds are you trying to control over how large an area?

  5. GreenEngineer, please understand this is not just *my* assessment of sheet mulching. This is based on my reading of the scientific literature on the topic. (That’s why I included the link to my review article, so you can see the references.) I also have lots of anecdotal experience with sheet mulches, and I still maintain that there is no point in using them, when thick layers of coarse organic mulch are less problematic and more effective. And I really don’t understand how sheet mulching can be embraced by permaculture as “working with nature” when it causes the types of problems I’ve documented. Why not just leave the newspaper and cardboard out? They’re hardly “natural.”

  6. What are you suggesting as alternatives for the first year of replacing weedy lawn with mulched beds? We’ve done a lot of this recently, and while imperfect, a layer of newspaper under the mulch does seem to have the best results.

    Herbicides only get what’s growing at the moment, plus the drift and toxicity bother me.

    We tried plastic for a while, but since you don’t mulch over it, it blows more than the newspaper. Plus, it takes quite a while, even in the summer, and forget about having any success in the spring or fall or in a shady area.

    Digging is terrible work over a large area, and, again, doesn’t get everything. Plus the fresh mulch makes a good nursery for the roots you missed to re-sprout. Also, what do you do with the removed sod? You tend to end up with a sunken bed.

    Just putting down thick mulch without the sheet beneath didn’t seem to do anything at all – the lawn was coming through it as though it was fresh fertilizer in a month. (We did put it down in spring…maybe a less hospitable time of year would have worked better?)

    So, we’re here at sheet mulching. I put a layer of newspaper over existing grass and weeds, and thick mulch over that. It seems the weeds that do come through are weak and spindly and easy to pull. The ‘sheet’ also seems to be mostly broken down after the first winter. I can’t imagine adding more paper after the bed is established – just more mulch.

  7. PlantingOaks, I’ve replaced our entire lawn with other plants. We mowed it flat (especially in the summer, when it’s dormant) and layer on a foot of wood chips (believe me, lawn does not come back through a foot of wood chips). We let it sit. In the fall, we pull it back and plant. We don’t remove anything – just let it degrade.

  8. A foot?! That’s a lotta chips! I have no strong opinions one way or the other on the merits of sheet mulching, but I am interested to hear more about a foot of wood chips. Assuming they weren’t composted, did any nearby trees and shrubs show signs of N defficiency? If not, why not? I think in the Kousa decline mystery, you said you had a soil test done and nothing was out of whack. Were there any other side effects (positive or negative) to a foot of chips on your once grassy area? (And I still love your fence :))

  9. Here’s my guide to sheet mulching that GreenEngineer mentioned:
    http://garden2table.blogspot.com/2007/04/how-to-sheet-mulch.html

    To answer your question about why permies would use sheet mulch: Because it works when it’s done right.

    It’s unfortunate that a few folks misused and then maligned the technique. The most common failure mode – like the situations you cited – is not using enough material – the sheet or the mulch.
    The sheet is important because it supresses many weeds from coming up. It doesn’t work on all of them (ex. Bermuda grass will come right through).
    If you can lay down a full foot of mulch and don’t have any really pernicious invasives like English ivy, Scotch broom, giant reed or Himalayan blackberry, it will probably work fine.
    In sloped situations, the sheets can also direct water into the soil.

    The essence of permaculture, IMO, is paying attention to what the land wants and then using the minimum input to achieve it and meet human needs. Sometimes, for me, that means using a sheet mulch. Sometimes it means digging a mulch basin. Sometimes it means building a swale. The really important thing is to listen to what that particular piece of land wants (this is a big part of permaculture training), find the tell-tale signs of its history and figure out what tools and techniques will work. But it has no one-size-fits-all solutions and won’t save you when you misapply techniques or fail to maintain work.

  10. Paul, I have an article on using a foot of wood chips in a restoration site. I’ll upload it to the original post sometime tonight. This article discusses suppressing perennial weeds, like blackberry, while at the same time vastly improving installation success using nothing but wood chip mulch. What interests me about the discussion about sheet mulch is that people cling to the idea, even when evidence shows it not to the best method. Science is constantly changing as the knowledge base improves; for instance, if some other mulch method was thought to be superior to thick, coarse organic mulches, I for one would investigate it, as would many other science types. And then change my mind if the evidence was convincing. I would hope permaculturists would do the same…

  11. The disconcerting thing to me, is the number of Extension publications and canned workshops out there touting the Lasagna or Sheet Mulching methods, especially in the area of creating a new bed – landscape, perennial or vegetable. We’ve put together workshops as part of a “Plan in the Fall for Next Year” process touting it as an excellent, sustainable method that is inexpensive, and ‘organic’, too.

    So, in that context, even though the foot of wood chips method is best (under current knowledge), does the sheet mulching/lasagna method fall into OK, but not best, or is it actually detrimental, in which case we should start revising all Fact Sheets accordingly?

  12. Ray, I would say that sheet mulching as a long-term strategy for weed control is detrimental. Without a doubt, sheet mulches decrease water and gas transfer between the soil and atmosphere. The anaerobic conditions imposed on the soils underneath sheet mulches are well documented – in fact, one of my colleagues promised to forward me some studies showing how sheet mulching is an excellent way to sterilize soil. So I guess if you want to create sterile soil conditions (i.e. for a vegetable garden), it might be acceptable. But I certainly wouldn’t use it in any sort of permanent garden or landscape where you have desirable plants on site.

  13. Dang. Compost Tea, Red Mulch, and now Lasagna Gardening. It’s hard enough learning stuff. Now I hafta unlearn it. 🙁

  14. Ray, if it helps at all, it’s fine to use shredded newspaper as part of the mulch layer. It’s just the two-dimensional materials that obstruct water and air movement…

  15. Wondering if this is another climate related argument?

    Permaculture has its origins in dry climates with poor soils like Australia. In these climates (and my own) any increase in organic material will increase water retention. Weed barriers are important because with irrigation these climates have no dormant season for weeds.
    By composting the weeds (in the rainy season)and retaining the soil moisture and biomass those weeds have absorbed you use less water and fertilizer when you start a new garden.

    I would like to see the evidence that you have for sheet mulching increasing water loss. Can you link it?

  16. The trouble with using newspapers and especialy cardboard in Australia is it attracts termites to your home but it is good for the garden as long as it is used away from the house.

  17. Keith, my original posting mentioned the issue with termites and sheet mulch, but I’m confused on why you say it’s “good for the garden.” Please include some detail on this.

  18. Hi Linda,
    I’m not sure on what you are basing your observations. We sheet mulched hard rocky/clay serpentine soil that previously required a crowbar to dig a hole and in which all of our plants had difficulties surviving prior to the mulching.
    One year on and we can dig the soil with a spade. The carbon content and soil moisture have improved dramatically and the plants are thriving. It is as if we added tons of manure to the soil rather than discarded cardboard and 50 mm of mulch hay.
    Sheet mulching stops unwanted plants, attracts and retains soil moisture and is not anaerobic. It is just not like covering the ground in plastic.
    Clearly you are mistaken.

    1. Part of Permaculture ethics is to use whats available, there is a difference between buying a bunch of cardboard and using what you have. it is more sustainable to use what you have available than going to home depot and buying wood chips shipped from a different part of the country.

      yes cardboard is not natural per say and there can be issues with toxins in newspaper ink/cardboard, however i avoid cardboard not produced in the US, as China has issues with toxins in cardboard and newspapers that dont have color or inserts use more eco friendly soy dyes. I do agree that all things being equal i would not use cardboard. But the fact is, if they are already at your home it is a much better use to use it in your garden then send it to the recycling center hundreds of miles away.

      I have used sheet mulching in combination with nitrogen fixers like clover to keep other weeds at bay. If you sheet mulch and then 3 years later have done nothing else then yes you will have weeds infiltrate it as they blow in the wind, dropped in bird droppings and creep into it over time. If you leave a open space nature will attempt to fill it regardless of mulch choice.

      Yes if you have cardboard and newspaper exposed they will dry out and blow away, however thats why i dont have it as the top layer……

      Part of sheet mulching or any mulching is the need to over time continue to add to and redo what was done in the past. through proper sheet mulching you encourage healthy microbial growth (i add soil ammendments like horticultural molasses to encourage this and add over time as well) and brings worms to the area that love the cardboard amongs the other composts you put in leaving castings and air pockets throughout. over time you can build up inches and inches of topsoil, much cheaper than unsustainable topsoil drop offs and watching it wash away every rain squall.

      1. There is no credible published evidence that sheet mulching provides any of the benefits you mention. If you are trying to mimic nature, why would you use a mulching material and process that is so unnatural? Observe how nature creates a mulch layer in a forest (woody debris and needles) and try to recreate that.

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