Basic Sheet mulching technique
Sheet mulching is one of the basics in the ecological gardener’s tool kit. It’s a method of eradicating weeds and building soil that eliminates herbicides and avoids tilling, both of which rupture soil ecology. Sheet mulching is a variation on nature’s way of building soil by accumulating and breaking down organic debris from the top down.
In its simplest form, sheet mulching is a two-step process:
- First, apply a layer of weed-suppressing newspaper or cardboard (or even cloth or wool carpet);
- Top it with about a foot of organic mulch.
Ideally this is done in fall, so that the mulch rots to become humusy earth over the winter. Also, the weed-stopping layer breaks down enough to let spring-planted seeds and transplants thrust their roots deep into the earth.
They are many recipes for sheet mulch. Here is below a graphic presenting another one:
“The cheapest place to store water is in the soil. (…) The key to the soil’s capacity to hold water is organic matter. Research shows that soil with as little as 2 percent organic matter can reduce the irrigation needed by 75 percent when compared to poor soils with less than 1 percent organic matter.” Tody Hemenway – Gaia’s Garden
Bill Mollison’s Technique
Extract from Bill Mollison – Permaculture 2. I like this one as it includes food scraps:
The first thing to say about sheet mulching is that it saves a great deal of labor, and a great deal of water, while dispensing with material that normally goes into landfill. Thus mulching also saves money for public authorities, and produces an excellent soil. Another appeal is that the system is tool-free and suppresses all weeds: ivy, onion and spear twitch, kikuyu and buffalo grass, docks, dandelions, oxalis, onion-weed and even blackberries. Before starting, plant any large trees or shrubs from the nursery as usual.
The first step is to sprinkle the area with a handful of dolomite and a handful of chicken manure or blood and bone; the latter two add nitrogen to start the process of reducing the carbon in the following layers. Don’t bother to dig, level, or weed the area. Your first attempt should be very close to the house, preferably starting from a foundation or path which is itself weed-free. Thus, you are protected from invasion of weeds from the rear, so to speak.
Now, proceed to tile and overlap the area with sheet mulch material. This can be cardboard, wallboard, newspaper, old carpet, old mattresses or clothing, rotted palings or thin wood. If you have a garbage bucket of non-noxious wastes like tea-leaves, peelings, leaves and small food scraps, scatter these first, for the worms. If you have a source of weed-seedy hay or like material, bury this also below the overlapped material, so that no weeds follow on.
Cover the area to be mulched completely with the cardboard or newspaper leaving no holes for weeds to poke through. If you have a valuable tree or shrub in the way, tear paper half across and pull it around the stem. Serve another, at right angles to the first. Go on, leaving only valuable plants (some dandelions, clover, useful small plants) with their leaves poking out.
Water this first layer well, and then apply, in sequence:
75 mm of either:
- horse-stable straw
- poultry manure in sawdust
- seagrass or seaweed
- leaf mould or raked leaves
- or any of these mixed.
All of these are manurial, or contain essential elements. All hold water well. Follow these with dry, weed-seed-free material on top:
150 mm of either:
- pine needles
- casuarina needles
- rice husks
- nut shells
- sea grass (Zostera)
- leaf mould or raked leaves
- cocoa beans
- dry straw (not hay)
- bark, chips, or sawdust
- or any of these mixed.
FINISH. Water until fairly well soaked. Always put at least 225 mm of cover over the paper, cardboard etc. 300 mm is better, 375 mm too much, less is of no use, so do a small area very well, not a large area thinly or sloppily. It takes about 20 minutes to cover an area some 10m2, and if you have all the materials at hand it is no trouble at all, and looks very well.
Planting right away…
Now, take large seeds (beans, peas), tubers (oca, potato, jerusalem artichoke), small plants (herbs, tomato, celery, lettuce, cabbage) and small potted plants.
Set them out as follows: With your hand, burrow down a small hole to the base of the loose top mulch. Punch or slit a hole in the paper, carpet, etc. with an old axe or knife. Place a double handful of earth in this hole, and push in the seed or tuber, or plant the small seedling in it. For seeds and tubers, pull the mulch back over. For seedlings, hold the leaves softly in one hand, and bring the mulch up to the base of the plant.
O.K. instant garden. Time to retire. An important thing to do is to quite fill up the area with plants, according to the prior planting plan you had worked out on paper. For instance:
- chamomile and thyme near the path;
- larger herbs behind them (marjoram, sage, comfrey);
- potatoes and tubers behind this;
- small fruits and fruit trees at the outer border.
Any ‘holes’ can be filled with strawberries, cloves of garlic, onion plants, potatoes, or some such useful plant, at random.
If you must use small seeds, do it this way:
Pull back the mulch in a row; lay down a line of sand, and sow small seeds of radish, carrot, etc. Cover with a narrow board for a few days, until seeds have sprouted (or sprout them first on damp paper). Then remove the board and draw mulch up as the tops grow.
Root crops don’t do well in the first year, as the soil below is still compacted and there is too much manure, so they tend to fork out. Plant most root crops in the second year, when it is only necessary to pull back the loose top mulch to reveal a layer of fine dark soil.
By the end of the first summer, the soil is revolutionized, and will contain hundreds of worms and soil bacteria. Just add a little top mulch to keep levels up, usually a mix of chips, bark, pine needles, and hay. Scatter a little lime or blood and bone. For permanent beds, do no more, but annuals need occasional fresh mulch after harvest: their wastes are “tucked under” as are all your food wastes from the kitchen. Worms are so active that the leaves and peelings disappear overnight. Leather boots take a little longer, and jeans a week or so and dead ducks a few days.
The same approach can be used to contain useful rampant species, so that blackberries can be confined to openings in forest, cumbungi (reedmace) to pond edges surrounded by ti-tree, and mint confined by shady dense bushes, rather than in tubs. Hens make a mess of mulch, but ducks can be released in mid-winter to clean up slugs and snails. Sawdust protects from slugs, lizards and frogs from woodlice and earwigs.
There is no need to rotate plants in this system, or to ‘rest the ground’. Potatoes are simply placed on top of the old mulch, and re-mulched. But then, there is no need to leave room to hoe or dig either, so plants may be stacked much more closely, but preferably in mixed beds rather than in strict rows. By frequent and random replanting, the garden will start to assume the healthy appearance of a mixed herbal pasture. The reasons for this “untidy” approach are relevant to pest control.
Nine Simple Steps to Sheet Mulching
Extract from Perennial Vegetables by Eric Toensmeier.
- Mow or cut your lawn, weeds, or other vegetation right down to the ground.
- Plant any crops that will require a large planting hole (including woody plants, perennials in large pots, and large transplants).
- Add soil amendments (as determined by your soil test).
- Water the whole area thoroughly. You are going to be putting a layer of cardboard or newspaper over it, and rain and irrigation won’t soak through very well until that weed barrier breaks down. Water also helps the decomposition process get going.
- If you have compost materials that may contain weed seeds (like fresh manure, leaves, or hay), spread them in layers on the ground. Put a dry, carbonaceous layer of hay or shredded leaves below any manure layer. Avoid thick layers, and make sure to get a good carbon-to-nitrogen ratio just as if you were building a compost pile. Water this layer well.
- Lay down a weed barrier. I prefer to use large sheets of cardboard from appliance stores, because these last longer and are quicker to lie down. You can use layers of wet newspaper too. Make sure to have a 4- to 6-inch overlap where sheets meet so buried weeds can’t find a route to the surface. If you have already planted crops, or have other preexisting plants, don’t mulch over them. Cut holes in the cardboard to make some breathing space for each plant (or leave some room around each plant when laying newspaper).
- Now you can add your weed-free organic materials. I like to keep it simple, and just add a nice layer of compost. You can also do some sheet composting here, alternating layers of nitrogen-rich materials like fresh grass clippings with carbonaceous materials like weed-free straw.
- Now you add your final top mulch layer, at least 3 inches thick. Water the whole bed thoroughly once again. Your sheet mulch bed is complete.
- You can plant right into your bed if you like. To plant tubers or potted plants, just pull back the top layers until you get to the weed barrier. Cut an X in the cardboard or newspaper. If you are transplanting a large plant, peel back the corners of the X. Throw a double handful of compost in the planting hole and then put in the plant. Pull the layers and top mulch back around the plant, water well, and you’re all set. Planting seeds is easy too. Just pull back the top mulch to the compost layer and plant your seeds. You may want to cut through the weed barrier below first, depending on weed pressure below the barrier. If you are planting seeds, be sure to water regularly, as compost on top of cardboard can dry out quickly.