Before I start, a bit of clarifying on the term ‘sheet mulching’ as it seems to vary depending on where you are in the world. In Australia, sheet mulching is different to no-dig gardening, although they’re very similar – one is an extension of the other.
- 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….
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.
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.
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.
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.
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.
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.
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.
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.