It's fall and my thoughts turn to lasagna mulching the garden beds to retire them for the year. I've had the chance to observe the effects that a few years of lasagna mulching have had on our garden, and wanted to share those observations with you.
First off, let's review what lasagna mulching, also known as sheet mulching, consists of. The basic practice is to cut down any vegetation to the soil line, but leave all plant material lying in place. You might not want to do this if there are lots of obvious seed heads on weeds. While lasagna mulching certainly curtails weeds, I don't like to incorporate weed seeds, which can lie dormant for ten years or more, into the soil any more than is unavoidable. Any vegetation other than seed heads is great - just extra organic matter. The next step is to add soil amendments. These should be tailored to what your soil needs. I use finished compost obtained from our township, wilted leaves of comfrey grown on site, our half-finished compost, a bit of greensand to help loosen our clay soil, and sometimes fresh manure laid down in situ by our laying hens. Next comes a covering of paper, newspaper, or cardboard. If using any kind of paper, it should be thoroughly soaked before or after being laid down, to help it conform to the contours of the soil. The heavier and thicker this layer, the longer the weed suppression will last, and the less frequently you will need to repeat the entire process. Finally, a good layer of wood chip mulch covers the paper. Again, the more of this you can pile on, the longer it will last and the better the weed control.
Some gardeners will actually repeat these layers in one go - thus, multiple layers of compost, paper and mulch laid down on the same day. I have never had the luxury of having so much material to work with. But if you have a small area and sufficient materials to do so, why not? On the other hand, I omit the soil amendments when working on areas that I never intend to plant in, such as walkways in the garden and border areas where I only want to suppress weeds.
My first motivation for lasagna mulching was exactly that - weed control. This is something that the technique accomplishes with great success. There are a few weeds that can make their way up through even a freshly laid section of lasagna mulch, and some airborne seeds that will land on and germinate in the wood chip layer, but those few are generally easy to remove by hand. What I wanted to discuss today though are the additional benefits of lasagna mulching. There are several of them that I've observed so far.
Significant soil improvement is one of them. This isn't exactly surprising; it's routinely mentioned as the "other" benefit of the technique besides weed control. But knowing intellectually that it would help the soil didn't quite prepare me for the fat earthworms I've been coming across. They're not inordinately long as worms go, but they are rotund. Wider than a pencil by a long shot; embonpoint, even. I hope it's not the case that the obesity epidemic has now spread as far as earthworms. But clearly these worms aren't going hungry. Their presence is both an indicator of healthy soil as well as a guarantee that the soil will be even better over time. Every earthworm is a mobile factory of soil fertility, and I count each sighting as a blessing. I also see, year by year, healthier plants that are better able to withstand the vagaries of stressful growing seasons.
The other benefits of lasagna mulching all have to do with what I believe are leading indications of the changes that global climate weirding are going to bring to my region. More than one model of climate change that I've seen predicts routine summertime drought across much of the US. My immediate region is forecast to escape the worst of this trend, but still the summers could still be drier than they historically have been. The last two summers here certainly have been that way, whether or not they were part of an emerging new pattern. Mulching and good organic content in the topsoil are critically important for plants dealing with water stress. Mulching because it curbs evaporative loss of moisture. And high organic content because organic matter acts like a sponge, soaking up water and releasing it slowly as plants need it. Lasagna mulching provides for both of these.
The flip side of the dry spells predicted under the climate change models is a pattern of more violent storms. This may seem contradictory, but it really isn't when you look at the meteorological explanations. Namely, a more energetic (warmer) atmosphere that is able to carry and move more water vapor. And in any case, whether it makes intuitive sense or not, this is exactly what we saw this year: About ten weeks of rain too insignificant to help the garden crops followed by a hurricane and a tropical storm that washed out roads, flooded farmlands, wiped out crops, and carried topsoil straight into the waterways, not to mention killing a few people and destroying a few homes. Our garden certainly took damage from these storms, and we had standing water in the portion of our backyard that is just barely lower than our garden. But careful inspection of the garden itself proved that we lost no topsoil at all to the heavy rains. Again, I believe credit goes to the lasagna mulching.
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| Phallus rubicundus (yes, really), red stinkhorn mushroom |
It wasn't just that the paper and wood chip mulch protected the soil beneath them. Within a few short weeks of laying down these materials I can find evidence mycorrhizal mycelium colonizing the entire area. These are networks of fine hair-like structures, the fungal equivalent of roots. The white threads are easily seen near the surface, knitting the soil together in an enormous net. I know by the wide variety of mushrooms that fruit out of those networks that we have at least a dozen different species of mycelium at work in the top layers of our garden soil. I take this as a spectacular indicator of biodiversity and the increasing health of our soil. Although I started lasagna mulching for weed control, the practice would be worthwhile even if the mycelium were the only benefit. If you wonder why I think so highly of mycelium, I refer you to Paul Stamets' eye-opening, jaw-dropping book, Mycelium Running
. Fungi of all types provide invaluable services to other life forms in the topsoil. They mitigate stresses on plants, break down tough organic matter into materials accessible to other organisms, move critical soil nutrients from areas of excess to where they are deficient, and can even bind up harmful substances (such as salts) in a waxy coating so that they become inert in the soil. Truly, mycelium is a blessing in the garden, and observation has convinced me that lasagna mulching equates to laying out the welcome mat for the fungal kingdom. |
| Unknown mushroom. Enlighten me? |
Finally, there's the fact that lasagna mulching entails a bit of carbon sequestration. That means, on balance, that we're taking carbon that could otherwise end up in the atmosphere (where it could do us further harm), and locking it into organic material in our soil (where it can do us some good). The amount of carbon that I manage to store away on our property may seem trivial. And in fact, it is. But the truth is that an acre of topsoil is capable of holding more carbon than all the air directly above it, all the way to the outermost edges of our atmosphere. But that carbon has to be stored up by and in living things working with plenty of resources in healthy soil. If the project were undertaken on a wide scale, boosting the organic matter stored in our topsoil and the living woody plants above it could go a long way to ameliorate the carbon emissions wreaking havoc with the climate; earth is populated, after all, by carbon-based lifeforms, and that's what organic matter is. My infinitesimal contribution is to do what I can with the soil I have some control over. You could do the same. I believe we will never solve the many problems stemming from industrial society's waste streams (and there are obviously many) until we look at the "wastes" we generate as resources so valuable that people compete for access to them. It's a challenge for me to lay my hands on enough cardboard, newspaper and wood chip mulch to cover all the areas I would like to, and this despite the fact that several people save their newspapers for me, and I know where to get cardboard and mulch for free.
Having outlined the benefits as I see them, I'll share a few tweaks I'm making to the way I use lasagna mulching. I've tried planting seedlings into a freshly lasagna mulched bed in the spring and found it problematic. While the plants survive, they don't grow particularly well without a great deal of hand-watering. The layers of paper soak up so much water that relatively little of it reaches the roots of the plants. The dry summers the last two years haven't helped. I have to water directly into the hole I punched through the paper layer to plant the seedling. This entails far more work than I would like. Fortunately I find no such difficulties in beds that I lasagna mulch in the autumn. By spring the paper layers have broken down enough to let water pass more easily through them, although they still provide something of a barrier to weeds. So I'm going to do my best in future to lasagna mulch my garden beds in fall, and the borders and pathways in spring or summer. I'm also sold on letting the chickens participate in the lasagna mulching process as often as possible. They enjoy their carefully orchestrated visits to individual garden beds that I'm done with for the year, it saves me that first step of having to clear the weeds, and they boost soil fertility by lightly tilling in their own manure.
One possible drawback to lasagna mulching is that the moist conditions it fosters just under the surface can be a boon to slugs and snails. This was apparent in 2009, the last wet year we had. The past two summers have been quite dry for us and I saw very few slugs anywhere in the garden. If I lived in a wetter climate I might look for some other technique to build our soil. Here in Pennsylvania I'm comfortable using diatomaceous earth to control what slugs and snails we have in wet years. And if the climate change models are correct, we're not going to be contending with wet summers very often.
Well, there are my reflections on lasagna mulching, after using this technique in my gardens for about three years. I think it's making enormous contributions to the health of my garden soil while saving me a lot of effort in weeding. I'll do my best to keep that in mind as I try to get all the mulching done this month.
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| Cyathus striatus, fluted bird's nest mushroom |
