Sheet mulching, also known as lasagna gardening, is touted as one of the most effective methods for establishing a no-till garden. Its layers of weed-smothering cardboard or paper, nitrogen-rich organic matter, and thick carbon-rich mulch are designed to break down into rich, loose soil. I have had a great deal of success with this method in both Northern and Southern Ontario gardens—but every so often someone who attempts it is disappointed.
As with any technique, sheet mulching cannot be applied the exact same way in every environment. The most common problems practitioners encounter can be resolved by adapting it to their own climate and site.
To write this article I have delved deep into permaculture forums across the internet to learn what problems growers have run into with sheet mulching. Here are the most common complaints and solutions that can help you avoid the same issues.
Jump ahead to a specific problem
- The sheet mulch did not deliver on its promise to loosen compacted soil
- The thick mulch layer stops light rainfall from reaching the soil
- A newly established bed dries out between rains
- The mulch slows the process of thawing frozen ground in the spring
- Water pools in your sheet-mulched area
- Sheet mulching attracts small creatures
- You’re worried that chemicals in the newspaper or cardboard will be unsafe for your garden
- You still have weeds coming through your sheet mulch
The sheet mulch did not deliver on its promise to loosen compacted soil
Some anxious growers have expressed dismay that their attempt at sheet mulching didn’t cure the compacted soil below it. Since this is a significant selling point of sheet mulching, they are understandably disappointed.
One factor that may be at play here is simply time. A season or two is not enough in most environments to see an appreciable difference to the soil below the sheet mulch. However, as the layers of mulch break down and become food for worms and microbes, those busy creatures will increasingly tunnel down through the layers of soil, performing nature’s version of tilling and creating channels where nutrients, air, and water can penetrate.
Another factor, particularly with clay and other compacted soils, may be that the grower did not plant any deep-rooted crops. An important fact to know about soil life is that nearly all of it centres around the roots of living plants, which exude valuable carbon sugars. If there are no roots penetrating below the mulched area, the creatures will have no interest in performing their tiling services that deep.
The best way to quickly break up compacted soil is to use sheet mulching and grow plants in it that will reach deep and begin the work of breaking up the soil with their roots. Perennials are a great choice because they will remain year-round and continue growing their network of soil life. Other popular choices are turnips and radishes, especially the long-rooted daikon radish. These crops muscle into hard soils and bust them open. You can even leave the first crop to rot in place; the vegetables will give their nutrients back to the soil life while the spaces left by their softening bodies allow water and air to penetrate.
It’s also important that the soil ecosystem you are nurturing remains healthy, so be sure to maintain a layer of fresh mulch on top as the layers break down. Wood chips are an excellent mulch choice as they attract fungi, which are important members of the soil-life network.
The thick mulch layer stops light rainfall from reaching the soil
This is an issue faced most often in drier climates. Even in more humid areas, though, an improperly laid sheet mulch can have rain infiltration problems.
First, make sure that you do not skip steps when preparing your sheet mulch. Soak the area where it will be laid a day before you begin work, or wait until a good, penetrating rain has done the job for you.
If your soil is extremely compacted, particularly if it is heavy clay, you can add a step and loosen the soil with a garden fork to help the water infiltrate. Push your implement into the ground then, keeping one foot on it, press down on the handle so that the tines lift up against the soil. Pull the fork out partway and repeat the action, then once more. Do this every square foot or so around the area you are preparing. A broadfork is a less common tool that is designed perfectly for this.
If you are preparing a larger area for a commercial operation, a keyline plow may be useful to rip an extremely narrow, deep channel that lifts and aerates the soil without damaging it the way traditional tilling would.
While you are putting your layers down, soak each one thoroughly. This soaking is your insurance against the problem of limited rain infiltration during the early months. The same thick mulch that keeps the rain out will keep this water in.
One common reason growers experience moisture problems is that they use dead leaves for their mulch without shredding them. The whole leaves form mats that are practically impermeable. When the leaves have been shredded with a leaf mulcher or lawn mower, the small pieces fall in all different directions with plenty of air pockets through which water can percolate.
If you are still concerned about the likelihood that you will have water infiltration problems, you can bury a soaker hose in your mulch layer for the first year. After that, your materials should be broken down enough that it won’t be a problem.
A newly established bed dries out between rains
A sheet-mulched bed is at least six inches above the surrounding soil when its layers are first put down. In a very hot climate, those exposed edges can contribute to excessive drying-out. To avoid this, practitioners in those regions recommend using sunken beds instead or, to maintain the no-till nature of the technique, to use borders around the beds. As long as the borders are as high as your layers, they will protect them from evaporation through the sides.
My region usually gets plenty of rainfall, but during a drought I experienced a similar issue. Merely covering the edges with a sheet of woody bark from a downed tree made a vast difference.
The mulch slows the process of thawing frozen ground in the spring
If your climate experiences cold winters with ice and snow like mine does, you may find that layers of mulch slow down the spring thaw. This is because the mulch blocks or even reflects the sunlight that would be absorbed into exposed soil.
For this reason, it is advisable to always wait until the ground is fully thawed before creating a new sheet mulch. If you want to speed up the thaw of an existing bed, you can cover it with a dark-coloured tarp that will absorb the sun’s rays just like the dark-coloured soil.
While you might complete your sheet mulch with a thick layer of shredded leaves or straw and wait for it to break down, you can also add soil on top to begin planting immediately. You’ll want to add a thinner layer of mulch on top to protect the soil, but this time you can mulch with compost to retain the dark colour. You can also darken lighter materials by mixing in charcoal, which is an excellent soil additive.
Water pools in your sheet-mulched area
If you receive more rainfall than your soil can absorb, water pooling may become an issue for you. This is most likely to happen on heavily compacted and clay soils where rain struggles to penetrate. Part of the sheet mulching’s ultimate goal is to improve infiltration, but it can’t achieve that if long-term waterlogging interferes with the process of decomposition.
If you suspect pooling will be an issue for you, avoid creating your bed in a natural depression where water will collect. If you are working on a slope, learn to identify its contour lines (lines on which all points are the same height above sea level). The internet has many tutorials for the simple A-frame method of mapping contours. Once you have established them, place your bed along one of those lines. Since all parts of it will be at exactly the same height, gravity will not cause water to pool at any single point.
Another option is to provide water with a place to go. You can combine the techniques of sheet mulching and hugelkultur by digging a trench and burying some wood beneath your bed. The wood’s ability to absorb and hold water will only increase with time as it breaks down.
Sheet mulching attracts small creatures
It’s true that the thick mulch may be attractive to mice and squirrels in the first year and, depending on your location, there may be predators who pursue them there.
However, as the mulch quickly breaks down, the creatures you are attracting should be nearly all desirable: earthworms, insects, birds who fertilize the garden as they hunt for them…and, of course, billions of microbes, which are the engines of a healthy soil.
You’re worried that chemicals in the newspaper or cardboard will be unsafe for your garden
Growers who delve into ink and paper processing are sometimes concerned by the materials that play a part in the manufacturing process of the paper, ink, or glue of newspaper or cardboard.
With very few exceptions, the consensus is that newspaper and non-glossy cardboard are entirely safe in a garden. The inks and glues are both plant-based and the most alarming-sounding chemicals you might read about, such as lye, are actually inherent to the wood rather than an additive. For a more fulsome discussion of the topic, I invite you to read this thread on permies.com where a number of individuals weigh in with expert knowledge.
You still have weeds coming through your sheet mulch
Another selling point of sheet mulching is its ability to smother weeds without removing the sod. Sometimes it doesn’t work exactly as advertised.
To prevent weeds, make sure that your pieces of cardboard or newspaper overlap each other significantly, and that each layer overlaps in different places. You don’t want to leave any cracks for plants to wiggle through.
In many cases, a few weeds will come up anyway because a gap opened up or because some seeds were present in your mulch. They will likely be spindly and easy to pull since they have worked their way through so much loose mulch to find the sunlight.
Wildfire, quackgrass, and overenthusiastic slugs
There are a few problems that may be more difficult to overcome in certain environments. If your area is at risk for wildfires, you may not be permitted—or it may not be advisable—to layer newspapers and cardboard on the ground. If you live in an area dominated by quackgrass, that particular weed has tricks up its sleeve to get under and around thickly mulched areas. And if you are in an extremely wet climate where slugs thrive, the addition of more damp mulch will only create more habitat for them. Ducks can manage a slug problem, but if you aren’t in a position to keep waterfowl then you may need a different solution.
In all cases, the best thing to do is to talk to other growers in your area. Find out what works for them and what doesn’t. You might find that living mulches and successional planting are the most effective, or another deep-mulch technique like the Ruth Stout method. But if it’s the right fit for you, sheet mulching is a great way to build rich soil and a thriving soil ecosystem.