Compared to the first two methods for improving soil.....compost and planting sweet potatoes......mulching can be a bit trickier. Problems can develop. The top mistakes I've made? (***disclaimer warning! These mistakes apply only to my homestead farm. The effects of mulching can be far different at other locations. Gee, even 5 miles away at my seed farm I see different results to my various experiments.) -------
1- Applying too thick a mulch atop dry soil, thus blocking out the rain. Since most of my rain arrives at under 1 inch at a time, the moisture never got past the mulch. The soil underneath stayed bone dry.
...remedy: while I could have removed the mulch, I opted to bring in water instead and pump it onto the land. Each day for three days in arow I trucked in 300 gallons of water, thus well watering the area. That solved the moisture issue and things progressed well from there.
2- Applying a mulch that creates a gley or biofilm layer that prevents wet from reaching the soil below. I once tried spreading a 12" deep layer of fresh grass clippings, then using a sprinkler, watered the area well. (note- I went a tad crazy when I purchased a riding lawnmower and spent a day mowing truckloads of clipping.) Yes, I got the soil beneath the mulch nice a wet. Over the course of the next couple weeks, the grass clippings matted down. Things looked nice. Then we got a heavy rain. When I checked the area the following day, the soil was only damp under the mulch. It looked like no heavy rain had touched it. But the grass clipping mat was soaked, slimy, stinky, and like a felted mat. It had not allowed the rain to penetrate, instead soaking it up and then having the excess find drainage channels. By the way, that grass was slicker than goose shit. One misstep and I'd be at risk of breaking my back in a nasty fall. Super dangerous.
...remedy: laboriously remove all that slimy, real heavy muck. I used it as part of the fill for some hugelkultur pits. Reapply a reasonable layer of mulch.
3- Using cardboard for mulching. While I still use cardboard to smother grass, I'm ultra careful around it. Cardboard can get super slippery when it's been wet for awhile, making it ultra dangerous to walk on. It's an accident waiting to happen. I was fooled initially. But after a couple of weeks, the wet cardboard began to get slick between the layers. The more I ayers of cardboard, the worse the problem seems to be. So now when I use cardboard, I never ever walk on it. After it is down for 3-4 months killing the grass, I will pick it up and throw it into a hugel pit or grow box. I don't leave it atop the soil as a mulch where I could walk upon it during a distracted or forgetful moment.
Above, I used cardboard topped with a bit of grass clippings to smother the grass around young coffee trees. It's time to remove it and replace it with a safer mulch to walk on.
Above, I've pulled some of the grass clippings aside to show the wet pasty cardboard layer below. Believe me, it's slick! No, I'm not going to film a demonstration video of me walking and slipping on that cardboard. Gee, I already have too many bruises that I'm recovering from due to other farm related knocks and falls. I pass on this one. Just use your imagination.
4- Using whole eucalyptus leaves for mulching. Like cardboard, these can get real slippery. But it doesn't take so long for it to happen. Once the leaves get wet, it's a case of slip sliding away. If I chop them up with the lawnmower, they don't get nearly as slic, and they decompose faster. So now I just suck them up with the lawnmower along with the grass. It turns out to making a decent mulch.
5- Applying too thin a mulch. The idea of a mulch is to protect the soil below from the wind and sun. When I spread a thin layer of mulch material, it was just a waste of time. When I went back and checked, the soil beneath it was too dry. I learned that too little mulch was just as much a problem as too much mulch. Nowadays I use 6" of fresh grass clippings, which settles down to 1 1/2" to 2" mulch layer.
6- Failing to renew the mulch when needed. This is still a failing on my part, basically because I always seem to be in need of more mulch than I have on hand. Over time the mulch settles down and starts to decompose. In most situations I really need to reapply mulch every month. And sometimes even more frequently than that.
So why does mulch help the soil improve so rapidly? I'm guessing there's a number of factors involved. Mulch helps keep the moist by preventing the sun and wind from drying it out. Moist soil is more hospitable to soil microbes, worms, insects, and other soil denizens. These critters physically move the soil particles about hither and yon. The mulch supplies food to a host of soil life, which in turn leave worm castings, waste, and "dead bodies" in the soil.....which in turn feeds more soil denizens. Ah, the circle of life. ----- At least, that's the way I figure it.
Regardless of how things are working, I see that mulch helps poor soil improve fairly rapidly. I've mulched areas where even grasses and weeds were doing poorly, and six months later the soil was ready for a garden. Hard compacted soil back in my rear pasture became for friable under a nice mulch of several months.
My mulching techniques for new areas.....
...in grassy or heavily weedy area, weedwack everything down (or mow it if that is an option). Then lay down one to four layers of cardboard depending upon how thick and aggressive the grass is. Top it with either a few inches of any kind of mulching material or a light covering of soil, enough to keep the cardboard for blowing away. After 6 months or so, remove the cardboard and start creating a garden.
...in areas with few weeds or where I have pulled most of the weeds out, skip the cardboard. Water the ground so that they soil will be moist. Top it with 6" of mulch. 3 months later, start creating a garden area.
One more thing ---- newspaper. I often use newspaper for a mulch the way I use cardboard. Using thick layers blocks the regrowth of grass and weeds, but it tends to get slippery just like the cardboard. But using only 1-2 sheets thick of newspaper with a mulch topping, I don't get that slick problem. But then, only new seedling weeds get smothered out. Some of the established tropical grasses come right through. So I find that using thin layers of newspaper isn't worth the hassle of trying to get it laid down without it blowing away. I get nice tradewinds where I'm located, so finding a windless day in order to use newspaper is difficult.
What else could I use for mulch? Just about any organic plant material as long as it isn't a plant that will root from the cuttings. Grind it up with a lawnmower or shredder, chop it with a machete or pruners, rake it up if it's already in small pieces like tree leaves. It's all usable.