sheet mulching

Sheet mulching – Issues and alternatives

Sheet mulching is a common practice recommended in permaculture. It uses cardboard and paper to smother the earth from growing weeds and grass whilst you attempt to build healthy soil on top of the cardboard and paper. My blog this month examines alternatives to sheet mulching which I feel are much more efficient and truly organic. 

Much is written in permaculture material on the benefits of sheet mulching, this web site is a good example. In some permaculture forums, such as this one, problems with the sheet mulching methods are also expressed. Lets work through some concepts before getting into alternatives

Sheet mulching

  • Removing organic matter – Step 1 with sheet mulching is to remove organic matter, in other words to smother weeds and grass with cardboard and paper so the growing space gets no light and those plants won’t grow.
  • Adding organic matter – Step 2 with the sheet mulching is to add very large amounts of organic matter on top of the cardboard and paper. By adding organic matter, the ultimate goal is to build healthy soil

Seems rather odd when you break it down to these 2 points. I remember a few years ago looking around a very experienced permaculture person’s garden and he showed me his sheet mulching efforts in his orchard. These involved a cardboard base, deep layer of sugar cane mulch, another layer of cardboard and more mulch. I said to him, it seemed like a lot of work and materials and asked why he bothered when his garden space was already in one of the most fertile locations in Queensland. Basically I was saying why not improve the base soil rather than using effort and imported resources to create new soil.

Sheet mulching issues

  • Introducing chemicals – The cardboard and newspaper introduce chemicals to the soil. Some of these chemicals are quite toxic. This forum thread on permies.com is insightful on chemicals in cardboard and newspaper. Also, check out a recent blog of mine about newspaper toxicity.
  • Recycling contradictions – Sheet mulching does recycle cardboard, some is likely to not be from your use. This is OK if your key principle is to recycle, but then to keep this principle, you have to then bring in a lot of organic matter to build soil on top of it, so basically you are negating the benefits of recycling
  • Ignoring the soil building nature of weeds – Weeds grow in soil to help with the soil healing process, to bring it into balance. Smothering weeds with cardboard ignores this fundamental process of nature. Instead of using what nature presents in your space, lots of work and materials (some toxic) are added to create soil, rather than working with nature’s process.
  • Aesthetic – Cardboard and paper in a space are prone to get untidy and will take quite some time to disappear. If you have a big rain event much of the cover material will be washed off the cardboard. Beauty in a garden is a fundamental feature of its success.

Alternatives to sheet mulching

  • Using weeds as resource – Your weeds reveal what is missing from the soil. By harvesting some of the weeds and turning them into a fermented tea, then applying this liquid back on the space, you speed up nature’s process. The success of this method can be improved significantly by using biodynamic compost preparations in the weed tea as these balance all the key mineral in the brew.
  • Growing a living mulch – Within your orchard chipping away grass around your planting area and then seeding it with a plant that will benefit the trees and out-compete with other weeds and grasses, such as clover, is a highly efficient way to use a simple living process. In a vegetable garden, you could grow a cover crop or even multiple cover crops. These will change the living state of soil to suit your needs and reduce weeds and grass
  • Re-mineralising the base – Getting your base tuned up with minerals is a big help. Low cost and easily accessible minerals such as gypsum, crushed basalt and wood ash always help
  • Stimulating soil life – In working with the base soil to transform it, I have found biodynamic soil preparations highly efficient. Using liquid fertiliser you make is also helpful, such as comfrey tea, animal manure teas, seaweed teas, etc. Again, the biodynamic compost preparations in these teas improve their potency. Be sure to incorporate compost into your activity but you do not need a lot of compost, so long as you include regular planting of green manure crops (for vegetable gardens). The living process in the soil is also affected by planetary factors and timing your soil management activities in tune with the planets, increases the potency of your work. This is a key aspect with biodynamic methods
  • Build a windrow compost heap – Built as your bed straight on top of the grass and weeds, this works well if you make a well structured compost heap.
  • Light mulching – Mulch the soil appropriately during the year, but don’t mulch too heavily. In this way some weeds will grow and the space will show you what it needs through the weeds, so long as you make potentised weed teas
  • Increase density of planting – By increasing your planting density in your vegetable gardens, you reduce the amount of light reaching the ground and the potential for weeds and grasses to grow. In addition, you get a lot more out of a small space

growing marigolds and nasturtiums

The image above is one of our vegie patches in Brisbane I started 4 years ago. On this 80m2 patch, I chipped off the grass and there was no top soil, only clay. I added minerals, spread a relatively small amount of old cow manure and some liquid cow manure, spread some forest mulch (non-eucalypt), grew our first green manure crop in the space and supported the soil with regular applications of biodynamic soil preparations. Whenever I planted into the bed I would plant my seedlings into our compost, I never had enough compost to spread over the whole garden.

So after 4 years, the soil depth has increased from zero to about 20cm, plenty deep enough to grow most vegetables and herbs. I imported no soil whatsoever and definitely no paper or cardboard mulch was used. I still get some weeds coming up and pull them out, make a weed tea or add them to a hot compost. It seems that many of the weeds growing now are edible. In all of these processes, nothing is added that has toxic chemicals and if I use manure, it must go through a biodynamic composting process before going onto the beds

I hope you can see that food gardening without sheet mulching is very possible. Our last 2 day biodynamic food growing workshop in Brisbane is on Nov 10-11. Come along, you will enjoy it, the practical insights above are demonstrated in my gardens where we host the workshop. More info here and how to register.

Happy gardening

Authored by Peter Kearney – www.myfoodgarden.com.au

Posted in biodynamic gardening, Fruit tree growing, urban agriculture, urban farming, vegetable gardening and tagged , , , , .

2 Comments

  1. A well presented argument but based on a false statement at point 1.
    Sheet mulching doesn’t remove organic matter.
    It creates compost under the sheet and adds to it above the sheet eventually creating a rich environment.
    Your comment about your friend having great soil already ignores the fact the he is still creating better soil.
    Another of your points that unless you are using your own cardboard negates the benefits is also flawed as by using other people’s waste still reduces waste to landfill.
    As for washing away in the rain…. Seriously Peter.
    By the way I don’t sheet mulch and agree 100% that weeds are a great soil building resource.
    I have built a beautiful 6 inch depth of soil on clay with nothing other than weeds, animal manure and mulch.
    Love your posts which I hope make people think beyond what they read on the internet and think for themselves.
    I’m sure you intend to be an agent provocateur.

    • Mark
      Thanks for the compliments, yes I do feel like a provcateur at times, started that way when I was a child and now I am 61. Like to respond on your points.
      1. Remove organic matter – the sheet mulching kills off the weeds and grass. What remains of this will go into the soil, but that does not mean it creates good compost. Good compost comes from a controlled process involving an array of inputs without chemicals, the cardboard leaches chemicals into the base soil with sheet mulching. If you dig up part of your lawn which has weeds and seeds on it, that does not mean its producing the type of soil you need to grow food. And yes, the statement of mine is provocative in the sense that you have to take something away with dead inputs with sheet mulching (killing the plant life) and create life again with a highly resource intensive process, when by fine tuning what is there in state, you could achieve a better result with less effort. I am highly pragmatic with my gardening
      2. With making good soil on top and often this is with the lasagna method, I have seen this result many times and it is nitrogen rich the first time, then looses substance very quickly, unless a lot more matter is added over time, thus continual bringing of dead matter, rather than using a living process. The “good soil” my friend wanted to create was likely to be loaded with chemicals, the matter he introduced had not gone through any hot composting process to burn up the nasties and even the mulch was from chemical farming, so that is not good soil in my book
      3. With the materials being washed away, I have seen this, in our extreme wet season. I appreciate that after a reasonable amount of time, things will bind together somewhat, but when I compare to using a green manure crop in our wet season, it just keep growing the more rain it gets and holds the soil beautifully.

      I will attempt to keep up my thought provoking posts. Thanks for reading.
      regards Peter

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