Sheet mulching (or composting) is the simplest, and least labour intensive, method of building the fertility of most soil types and affords the gardener an easier option than back-breaking spade work for establishing a new garden. It encourages the soil biota, many species of which will work the soil over for you – no digging required. It is a three-in-one method which combines composting, mulching and biodegradable weedkillers (cardboard and newspaper), and it enables you not only to improve your soil but to grow and harvest a crop all at the same time.
There are many ways of sheet mulching, two of which are discussed. Both require enormous volumes of organic matter initially and, thereafter, it becomes a routine activity in the garden to keep adding more mulching materials to the surface as the soil flora and fauna break them down into life-sustaining humus, and releasing nutrients which are gobbled up by the plants. The whole idea behind it is to minimise soil disturbance.
Here’s how to go about it:
Mark out the areas for your new beds and, right on top of whatever is there (bare soil, weeds, grass), sprinkle some rock phosphate or bonemeal and wood ash or dolomitic lime (for acid soils) or sulphur (for those alkaline Cape Flats soils).
Cover the area with a layer of manure to provide the extra nitrogen to break down the dead leaves and roots of the plants that will be buried by the mulching materials.
Then add alternating layers (6cm, or 3 fingers, deep) of green, wet materials (lawn clippings, fresh leaves and prunings) and brown, dry materials (untreated sawdust, autumn leaves, straw) and more manure, watering each layer as you go, until you have covered the demarcated area to a depth of at least 20cm. With vigorous Kikuyu grass it is a good idea to mulch the area up to 30 or 40 cm deep. You’ll be surprised at how much organic matter it takes to do this.
Cover the whole area with overlapping sheets of newspaper (3 – 5 sheets) or cardboard (1- 3 sheets) to prevent weed seeds from germinating, and grass runners from creeping through, and competing with your plants. Wet the paper and cardboard thoroughly and, in a very short space of time, it will have rotted down and disappeared, its job done.
Lastly, add a layer of compost, soil and mulch to hide the unsightly newspaper and, hey presto, you’re ready to plant. Make a hole in the mulch/soil layer, cut a cross through the paper or cardboard, add a dollop of good potting mix (half compost, half good garden soil) and plant your seed or transplant your seedling. Water well.
Mark out the areas for your new beds and cover whatever is there (bare soil, weeds, grass) with between three to six sheets of newspaper or one to three sheets of cardboard. Make sure the sheets are overlapping well and water.
Now proceed as above, layering green, wet and brown, dry materials and manure until the bed area is covered to a depth of at least 20 cm.
Add a layer of mulch to cover.
To plant up this sheet mulched area, simply make a hole in the mulch, add a good soil mix and plant.
In both cases there is no need to use herbicides or other drastic measures to kill the grass and other vegetation. The newspaper and cardboard will do it for you. A myriad different creatures will take up residence in this bountiful environment, enriching the soil beneath with valuable humus which will be worked in by earthworms and other organisms which are, in effect, digging the soil for you.