Kate at "Living the Frugal Life" has a great post on the merits and techniques of sheet mulching in the garden. Since this has been the key to soil improvement (and we have dreadful soil) in our garden, I wanted to highlight it.
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.
Most writers emphasize the merits of deep mulch for water retention, and those are very real. What I like about Kate's post is that it also mentions the rarely-noted quality that sheet mulch makes a huge difference where there is too much water. I don't just mean that it protects the garden from erosion, which it does, but areas that get flooded that are mulched simply do much better. We not only don't lose soil, but we don't lose as many plants to drowning. I'm not sure why - my guess is that the better soil structure makes it less prone to saturation generally, but the difference is quite remarkable.
I do find that have to rake off some of the winter's mulch in early spring for planting here, because it does delay soil warm up, but that is the only negative among many positives (I haven't even seen that we have more slugs and snails in the mulch, although ymmv).
My favorite benefit of all, however, is that sheet mulching permits people to do substantive garden expansions without any equipment at all - and now is the time to do it. Put enough layers of organic material on cardboard or newspaper over the winter and the material will both smother grass and weeds and break down enough to be plantable in spring. No digging, no painful sod removal, no tilling, no bringing huge quantities of weed seeds into the light. What's not to love?
Sheet mulching is even doable on a farm scale, we're finding. Rotting large bales of hay can be moved to our farm, combined with large quantities of goat and chicken manure (composted), brush piles and leaves left in bags on the street (the bags get laid down in long rows to mulch the beds) and while I can't cover acres, I can make signficant spaces for further production. With a bulldozer or a tractor I could do more, of course, a la Sepp Holzer's brush berms, but the results are pretty impressive already.
"Rotting large bales of hay can be moved to our farm"
eee! Beware beware of weed seed from problems you don't have- yet.
The voice of very painful experience here! In my case- a batch of pig manure spread in the garden- and 3 years later we gave up and moved the garden.
I don't think we have any weed seed problems we don't have yet ;-).
I haven't had much luck with sheet mulching as a way to way to start new beds. It helps suppress seed germination once you get to 8 or 10 inches of mulch, but the grasses and perennial weeds are barely phased. So YMMV. I solarize for 6 weeks, then mulch, then weed daily for a while, and finally Round-Up anything that has managed to survive. (Mostly lirope and violets.)
But vast expanses of mulch is practically my favorite garden thing!
One good way to reduce the weed seed problem is to have at least one really hot phase in your compost cycle. Our compost gets hot enough to be seriously uncomfortable, and we don't use anything in it to really raise the temperature. If you add green manure to the compost once it's partly broken down, the nitrogen kick can get the temperature up to the point where most seeds are sterilized.
I haven't had much luck with sheet mulching as a way to way to start new beds. It helps suppress seed germination once you get to 8 or 10 inches of mulch, but the grasses and perennial weeds are barely phased.
Sounds like you don't have enough "sheet" at the bottom of your sheet mulch - ideally you're looking for at least 3 layers of heavy-duty cardboard (or similar), overlapped a good long way. I've sheet-mulched over some really heavy-duty invasive grasses and perennial weeds with good results. Admittedly the equisetum is now starting to break through, but that stuff will grow through reinforced concrete...
Mike McGroarty (FreePlants.com) claims eight layers of newspaper is what you want; it is as good as landscape cloth for suppressing weeds, and you don't have to drag it out of the soil in later years.
So if you want to use newspaper, I imagine eight sheets thick is the goal, if not the minimum.
I've never found newspaper to be a great sheet mulching material - the sheets are too small to get enough overlap. Better than nothing, but not ideal in my experience.
What I have used to quite good effect is triple layer paper chicken-feed sacks, opened out. Again, you need to overlap them a long way to prevent the more invasive plants from sneaking through between the layers - I usually aim for 3 layers, fully overlapped.
Thanks for the mention, Sharon. Your point about lasagna/sheet mulching being a viable alternative to mechanical tilling is an excellent one that I neglected to mention in my post. Sometimes I get so myopic with my own practices that I forget to step back, think about, and point out all the benefits and reasons behind what I'm doing. Thanks for including that point.