Sheet Mulching

Dec 9, 2015

  • Sheet mulching is used to smother the ground with organic matter (generally cardboard, newspaper and woodchips plus some nitrogen materials including animal manures or blood and bone), usually to suppress grass in order to establish more desired plants. The desired plants are planted directly into the original soil through the sheet mulching with some compost if needed.
    • No-dig gardening also smothers the ground, however has many more layers of organic matter to create an instant raised garden bed which you can plant into the same day you make it. If you have really challenging soils and can’t plant into them, a no-dig garden can work great for you. Read about how to create them with the Australian City Farms and Community Garden Network.
    Righteo, lets start. We’ve been tweaking our young orchard lately to stop the grass from creeping in and taking over, something the fruit trees will hate, as will we. Grass sucks a lot of water and nutrient away from trees (and all other plants), so even if you choose to have grass throughout your orchard, your trees will be happier and healthier if there’s a good buffer from their trunk to where the grass starts. At our place we’ve got a range of invasive grasses which we’re slowing planting out to make way for a more productive landscape. After transplanting the asparagus understory from the orchard (there just wasn’t enough room), we’re now establishing perennial and self seeding floral understory to attract the pollinators, suppress unwanted plants and look good. To help all these plants thrive we’ve sheet mulched the whole area to suppress the grass and add a stack of organic matter. Here’s how we did it….

    IMG_5163Some grass moving in on our fruit trees… Grrrrr.

    IMG_5166

    Step 1

    Traditionally you don’t have to do any weeding before you start sheet mulching, however we wanted to really bang our invasive grasses on the head, so the first step for us involved going through our orchard and getting out as much grass as we could with our hands. If you’re starting with a blank canvas, i.e. a big flat lawn – mow the grass down really short and leave it on the ground (spread evenly). Pierce the soil with a garden fork to help water, nutrients and air find their way into the soil quickly. IMG_5164

    Step 2

    Next up we added some minerals and nutrients tailored to what our heavy clay soils need. This included gypsum to help bind the clay into aggregates, chook poo from our feathered friends, some old grass clippings and a bit of blood and bone. It is not essential to add inputs, but like I said, our soil needs it. IMG_5183 IMG_5187

    Step 3

    Place your ‘weed mat’ on the ground. We’ve used thick sheets of newspapers which *heavily* overlap, ensuring there’s absolutely no gaps at all – that’s a really important detail. You can also use cardboard boxes just remember to remove the sticky tape and avoid the waxed boxes as they’re harder to work with. We never use any glossy brochures/magazines as their chemical ink isn’t desirable for our soils. Before we lay the newspaper down, we soak it in a bucket/wheelbarrow of water, this helps it mold to the surface, prevents it from blowing it away and actually attracts soil critters to hang out around it – worms love it. IMG_5170 When it comes to the edges of your garden bed, be mindful that this is where weeds usually creep in, you can see below we’ve extended our ‘weed mat’ to go under the timber lengths to help slow the grass down. FYI, this edging of cypress macrocarpa branches is temporary, in the near future we have to dig up this pathway to install a water pipe, so we haven’t been overly ‘special’ with how we’ve built this edge. In time, we’ll be putting in some more solid hardwood timber sleepers. IMG_5191

    IMG_5192Note the overlapping of the newspaper – there should be absolutely no gaps for any weeds to sneak through. 

    Step 4

    The next step is to cover the newspaper with heavy mulch – we prefer to use woodchips (ideally ramial woodchips) for their high nutrient content and ability to create the right environment for fungi to thrive – other people prefer pea straw (or different types of straw). Below, you can see our espaliered orchard with the middle section half complete and the end closer to us finished off with woodchips. IMG_5194 IMG_5171

    Step 5

    Plant a useful understory. Where there’s space, why not plant something? We broadcast nasturitum, calendula, nigella, red clover, sweet alice and borage seeds. Within a few months this will be covered in colour and life – above and below the ground.

      IMG_5176Calendula seed above and nasturtium below.

    IMG_5177 Now, please be aware that sheet mulching is not the silver bullet to vigorous weeds. Generally they will still find a way to come back – just a lot more slowly. You still need to manually stay on top of things in the early days by the occasional weeding session. Eventually they will be overwhelmed and dominated by more desired plants, but in these early days when there’s heaps of sun and space they’ll keep trying to return. IMG_5179 While young, our orchard is already one of our favourite places on our property and has started to produce fruit and berries – which is why we hang out here a lot. Working with the soil (which sheet mulching is part of) will help the plant’s overall health and vitality, ensuring that this space will be nothing but beautiful, abundant and cranking.]]>

    your thoughts:

    13 Comments

    1. Peter Heffernan, PDC Lorinna.

      Wonderful sheet mulching demonstration guys.

      One tip regarding the weed mat material.

      I have discovered that the hardware stores that sell house paint have large sheets of cardboard that are tape, staple and ink free, that come from the delivery of pallets of paint tins. Each sheet is about one and a half square metres, and they are used to separate the layers of paint tins on the pallet. I’ve made friends with the staff members of several stores who are pleased to supply regularly.

      Reply
      • Hannah Moloney

        That’s a good friend to make Peter 🙂

        Reply
    2. linda

      RE sheet mulching — use lots of cardboard and/or paper or magazines/tabloids or anything made of paper. I flattened approx. 4 boxes and overlap them. Do not leave any cracks. Sheets decay quickly. Thicker sheets the better. Might last several months or a year. Depends how much you wet the sheets and rain and snow, even rocks and dirt and insects living and munching on sheets. Sheet mulching is hard work, but it’s better than thin, porous fabric weed barrier. Oh, before laying sheets down — REMOVE plastic shipping tapes, because when sheets decay — ugly tapes remain alive and well and pop up to ruin your garden.

      Reply
      • Hannah Moloney

        That’s right Linda – we often use cardboard as well. Although not any glossy magazines as the chemicals in the heavy inks they used are great for the soil. 🙂

        Reply
    3. Susan

      Hello, I have a 2m sq patch of Angled Onion Allium triquetrum. Unfortunately when I was just starting gardening a few years ago, I tried to remove it by digging out. Some bulbs were as big as garlic bulbs. I didn’t know about the “bulblets” being spread by my digging, both brown and white. Have you had success with sheet mulching this resilient weed? If so, was it many years? It is almost three years later, and I am still dealing with onion weed coming up each year. To make it worse, it is amongst and surrounded by daffodils.

      Reply
      • Hannah Moloney

        Hi Susan,
        I haven’t had to deal with this in particular- but plenty of other ones that keep come back again and again. I sheet mulch every spring to manage our twitch grass in our orchard. I actually think it’ll probably always be there as it’s so entrenched in our landscape. So – sorry, unless you excavate with pigs (or an excavator) you’ll probably always have it. Although 2m2 is so little I’d be tempted to just dig it up and sift the bulblets out. 🙂

        Reply
      • James

        Many gardeners I know of would consider soil with onion weed as ‘contaminated’ and remove it all. I have found that most plants will live with onion weed, so I just methodically remove the biggest ones every spring, until the outbreak is under control. Don’t let it get to you, onion weed removal is a looooong term project.

        Reply
    4. Zooey

      Ink from newspapers is very toxic. Use other (natural) materials . 🙂

      Reply
      • Hannah Moloney

        Hi Zooey. We use newspapers that use soy-based ink. You can call and ask your local newspaper what type of ink they use to clarify.

        Reply
    5. Dylan Villiers

      Hey Hannah,

      Just wondering where you source your woodchips from?

      Thanks,

      Reply
      • Hannah Moloney

        Hi Dylan, A range of places. Sometimes we’ll get chips from local arborists (as long as they don’t have weed seed in them and other times through local landscape supplies. These ones in the blog are fine woodchips from Hobart City Council’s landscaping section.

        Reply
    6. Na

      Hi Hannah,
      Thank you for such a helpful article on sheet mulching.
      We are about to sheet mulch (with cardboards) our garden bed which has established fruit trees (2 to 3 years old) on them. I am a bit concern regarding sheet mulching (with thick cardboard) around the fruit trees now as we are heading toward Spring/summer, would this prevent the rain/watering to penetrate through the cardboards to the root of the trees? Would this detrimental to the fruit trees as we are heading into The warmer months? As laid cardboards would take months to breakdown.
      Looking forward to your response.
      Many thanks in advance!
      Na

      Reply
    7. Katrina

      Hi Hannah, thanks for the very useful post. I’m planning some sheet mulching at our place in Meanjin. Question about broadcasting the understory seeds – do you just throw these onto the mulch or do you need to add another layer of soil or compost for them to germinate?

      Reply

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