Sheet Mulching

sheet mulching finished

This is a great way to create a weed free garden area which can later be planted, and if done properly, it is very effective. It is an ideal way to prepare bare ground for future planting, for making a new vegetable garden or for converting part of the front lawn into a garden bed.

Laying cardboard. This is covered with mulch at the end.
  1. Step one is to mow or scalp any existing weeds as low as you can.
  2. Step two is to feed the area with an organic based fertiliser and water it well. This is often a step which people skip, but it is really important.
  3. Step three is to cover it with a good layer of newspaper (no glossy magazines) – at least 15 sheets thick, but the thicker the better. A state newspaper opened in half is ideal. Overlap it properly to make sure there are no gaps, or the weeds will simply grow through. You can also use non-waxed cardboard however it needs to have all the sticky tape removed.
  4. Step four is to top it off with a good layer of bark chip mulch (20-30mm). If you plan to create a vegie garden above this layer, you can add weed free compost and the pea straw in top.

Now the last step is to be patient and wait for the weeds underneath to rot away.

If you do all the steps correctly, it is even effective against troublesome weeds like couch and kikuyu. For soft annual grasses it might only need 3 months, but for these running grasses, allow six months. Always inspect what is underneath this layer before you start planting and refrain from getting too eager to plant if there are any signs of living or white grasses or their roots, as if you cut through this layer and plant into the soil before the weeds have died, they will simply grow through the slits and in time take over the area you were trying to make weed free.

Laying cardboard with plenty of overlap

What happens is that the weeds try to grow due to the fertiliser and moisture, but there is no light, so they eventually rot away. If you lift the layers mid-way through the process to see what’s happening, you will see pale, even white growth on the weeds, as they don’t get any sunlight and can’t photo synthesize.

sheet mulching finished
Finished sheet mulching

Sheet mulching trouble shooting

Reasons why it hasn’t worked – all tried and tested multiple times at Sophie’s Patch 😊

• Weeds not fed and watered to start the process off. The fertiliser and water stimulate the weeds to want to grow, and it also helps the weeds rot. From mid-autumn to mid spring, this is not as important as you know the rains will come shortly but is essential over the drier months.

• Sticky tape left on cardboard – when you go to remove all the cardboard, you realise how much sticky tape is used in this world. Usually, it is on the edges of the cardboard and then when you overlap, the plastic strip prevents the layers of cardboard from binding together and running weeds like kikuyu simply sneak through the gaps.

• Not applying thick enough layers of newspaper or cardboard or not overlapping it properly. If you only used 6 sheets of newspaper, chances are it might break if you walked across it, and as soon as you have a break, the weeds will come right back. Similarly, if it only overlaps by a cm or so, the weeds will probably sense the light and escape out to it. They have a remarkable desire to survive and running weeds like kikuyu are Nature’s version of synthetic turf!?

• Hand holes in cardboard boxes. Be aware of any hole or cut out in cardboard when sheet mulching. If there is a hole. You will need another payer of cardboard underneath.

• Not being patient enough. I am always impatient to plant and where I haven’t waited long enough for the weeds to break down, and planted anyway, the weeds come back, and now they are in and around your plants and it’s a weedy mess. I have a large section on my driveway where this is exactly what happened, and the couch is everywhere through my plants. Now I need to remove any plant I want to keep, make sure there is no couch in its roots, pot it up for 6 months, re-sheet mulch the whole area for 6 months, and then finally replant. What a nuisance – if only I had been patient to start with.

• Installing garden art – often at Sophie’s Patch I have had sheet mulching in place and then used a star dropper to stand up a metal screen or similar. If the sheet mulching wasn’t finished, I just created an escape hatch for the weed!?

• Adjacent weeds creeping back in. Kikuyu is my nemesis at Sophie’s Patch and if I have sheet mulched part of an area and kikuyu remains next to it, it simply creeps back in. I can sometimes control this manually, but if I get too busy to be on top of things before you know it this running grass has taken over the area again. It’s my ongoing battle along our driveway where the kikuyu in the neighbour’s paddock keeps feeding back in.

Take it from me, it’s much easier to do it properly the first time!

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