Sheet Mulching for Beginners
Using Bill Mollison’s Recommendations
This season I began to put into practice what I had learned on the Permaculture Design Course about mulching and no-dig cultivation. I wanted to begin experimenting with this approach, not only because it saves hours of backbreaking work and minimises watering, but because it improves poor soil and suppresses weeds.
On our site we are dealing with thin soil, a thirty-degree slope, a big couch grass issue, and a tendency to back problems in the gardener, so it all seemed worth trying. Armed with what I had learned, plus further research into the recommendations of Permaculture guru, Bill Mollison, I set about creating new beds on land that had been uncultivated for at least 100 years, when the longhouse was last known to have been inhabited.
Wanting, as usual, to have everything done yesterday, I went at it with a will, and found local sources of cardboard and straw, got familiar with the scythe, and went in for quite a lot of quarrying to remove the many huge stones that lie both on the surface and beneath it on much of our plot.
Apart from attacking the huge tussocks that were the remains of old anthills, I did not dig. I used whatever came to hand as part of the green mulch – I scythed long grass and weeds, and a huge quantity of immature foxglove leaves all got absorbed into the process.
I now have a number of large beds all neatly tucked up with straw on top, ready to over winter, and, hopefully, become ready for cultivation in the spring. Peeking under the thatch of one the other day, I came across a slow worm – fantastic for dealing with the slugs. A number of toads seem also to like this habitat - all good news so far.
The method I used is a simplified one. First, scythe down the green growth and remove. Second – sprinkle with composted material from the heap. Sheet mulch with the cardboard, and sprinkle more compost over it. (This feeds the microorganisms that will break down the carbon mulch). Top off with all the green material that was scythed down (before it developed seed heads), then put a good layer of straw over all, and leave well alone.
As you will see from the following summary of Bill Mollison’s method, there are various substitutes for parts of this process – one that I found useful was bracken when I needed more green material – it’s high in potash. You will also see from the following notes how to incorporate planting into the process so you can begin using your sheet mulched bed right away if necessary, but note the advice to avoid root vegetables in the first season till the worms have dug the soil for you and the rich manure has mellowed.
The Mollison Method
Bill Mollison too points out that sheet mulching is labour saving, reduces watering, and uses material that often goes to landfill. It produces excellent soil, requires few tools, and suppresses weeds, including ivy, couch grass, docks, thistles, dandelions and even brambles.
Before laying down the mulch, he suggests planting any large trees or shrubs you might want to include by digging a spacious hole, and gently back-filling round the roots, ideally with a mixture of rotted manure and soil.
He advises sprinkling a handful of lime and a handful of chicken manure (or any organic high nitrogen manure) over the area to be mulched to start off the process of reducing the carbon in the subsequent layers (feeding the microbes). There is no need to dig, level, or weed the area - simply cover with sheet mulch material, overlapping the edges and leaving no gaps. The sheet material can be cardboard, hardboard, thick layers of newspapers, thin wood etc. Kitchen waste can also be scattered for the worms. If you have a source of hay containing seed heads, bury this below the overlapping material, so that no weed seeds can germinate, and leave no holes for weeds to poke through.
He advises working round any previously planted trees by wrapping the mulch around the stems. Valuable plants can be left with their leaves poking out. Water well and then apply 75 mm of either stable straw, poultry manure in sawdust, seaweed, leaf mould /raked leaves, or any of the above in combination.
All of these materials contain vital elements and hold water. Follow with 150 mm of dry weed-free pine needles, nutshells, leaf mould/raked autumn leaves, dry straw, bark, chips or sawdust or a mixture of these, and water well.
He recommends putting at least 225 mm of cover over the paper, cardboard etc. Up to 300 mm is fine, but the covering should not be more than 375 mm thick.
Planting your mulched bed
Large seeds, tubers and small plants can be planted using your hands to burrow down to the base of the loose top mulch. Alternatively, punching a hole in the sheet mulch allows the seed, tuber or plant to be planted through it. For large seeds like beans, and tubers, put the mulch back over. For seedlings, bring the mulch up to the base of the plant.
The Polyculture Approach
Sheet mulching lends itself well to what in Permaculture is called polyculture – as opposed to monoculture (growing one kind of plant in large numbers all together). This is a good system to have in your Zone 1 ie: near enough to the house to be convenient for a quick dash to the veg. patch. It is recommended to fill up the area with plants, and to make use of the varying heights of plants to achieve a stacked system that emulates what occurs in natural woodland. Any gaps can be filled with strawberries, cloves of garlic, onion sets, potatoes etc. at random. Small seed can be sown by pulling back the mulch in a row and laying down a line of sand or compost on which to sow it; then mulch up to the seedlings as they grow.
The method notes that root crops may not do well in the first year as the soil underneath is still compacted until the worms have tilled it, plus the rich manure can cause forking. If most root crops are planted in the second year, it will be apparent, when pulling back the loose top mulch, that a new layer of fine dark soil has been generated.
By the end of the first summer, the soil should contain a myriad of worms and beneficial soil bacteria. Adding some top mulch will keep levels up – and this can be a mix of chips, bark, pine needles and hay, with a little lime to regulate acidity. Worms should be so active that leaves and peelings tucked under the top mulch will disappear rapidly and give annuals a boost.
It is suggested that comfrey or other vigorous herbs be planted as a barrier around the area, and further mulching around it with cardboard, sawdust and straw will keep invaders out. (The same approach can be used to contain useful but rampant species like blackberries, so they can be confined to openings in the forest garden).
With the Permaculture no-dig, sheet mulched system there is no need for crop rotation, or to 'rest the ground' or to leave space to hoe or dig, so plants can be stacked closely in mixed beds (polyculture), thus maximizing yield. In this way, if there is frequent replanting, the bed will mimic a natural woodland habitat where symbiotic relationships between plants help their growth and resist pests, and where there will be a healthy growth of valuable mycelium below ground.
If strong weeds do get through, it is advisable to mulch with damp newspaper and a bucket of sawdust and repeat if necessary.
The requirement is to water only if plants wilt. If, on feeling down in the mulch, it is damp at the base, it doesn't need water. The only exceptions are newly planted seedlings.
Ongoing input requirements
Most of the work in a polyculture bed is infilling spaces with useful plug plants, and keeping the garden full at all times. Trees may never need fresh mulch, as larger trees and shrubs soon become self-mulching as in natural woodland; herbs can cope unaided, and only annuals need attention.
The advice is not to bury sawdust or chips, but put them on top where atmospheric nitrogen can break them down. Worms add manure to supply the base layer in the bed, and the mulch should be kept loose, with the addition of lawn clippings or sawdust mixed with stiff dry material like chips, pine needles, or bark.
If all goes to plan, you will enjoy increasing output with decreasing input – and I, for one, find that very sustainable!
Source for this summary is Bill Mollison’s Permaculture 1 and 2.