I've been exposed to a lot of dirt in my day. Sandy dirt, oily dirt, loamy dirt, political dirt, soggy dirt and my current trauma--clay dirt. When I want to do something productive with my dirt, I talk pretty to it and call it soil.
Soil is composed of 4 parts: minerals, organic material, water and air. The mineral portion in my current yard is nearly 100% clay. Clay particles are almost the exact opposite of sand particles. Sand, the largest of the mineral particles in soil, is crystalline in structure and will not bind together. Silt is smaller than sand. Clay is the smallest particle--more like squashed rice seeds that slide together and won't come apart. Really great dirt has a combination of sand, silt and clay as its mineral components. I don't have really great dirt.
Of the four parts of soil, the mineral portion is nearly half of the volume--about 45%. Normally, water makes up 20-30%, organic material makes up less than 5% and the rest of the soil body is "air." Gardeners really can't do much about the mineral portion of their soil. So we spend our time working on the last three portions in an attempt to create fluffy dirt.
Nearly every plant label I've ever read says something like "prefers well-drained soil." Well. Here in this particular piece of Western North Carolina, we have about a quarter of an inch of "topsoil" and a whole bunch of (currently) soggy clay. Just how, pray tell, am I supposed to create "well-drained soil" out of this?
Some folks would tell you to till in peat to force air into the soil. I'm not going to tell you that. The thing to do here is just provide an assist to Mother Nature, because she's going to be a whole lot more efficient than we could ever be.
This particular house site began as a lot scraped of any topsoil by the builder. Presumably, he threw down some grass seed after finishing construction. Based on the year of construction and the age of the trees at the edges of the lot, the only tree standing here at the time of construction was the black walnut. Everything else either volunteered or was planted since that time (about 30 years). Grass tends to impoverish soil--consuming the organic nutrients and not adding anything to the mix. Grass also doesn't provide much nourishment for soil insects, so those scraped areas weren't even getting the benefit from insect poo. So the best parts of the yard in terms of organic matter were the overgrown areas that were too hard to mow.
At time of purchase, in the midst of drought, it was hard to get a shovel into anything. So anything that wasn't going to be mowed was covered in newspapers or cardboard and then mulched. Drip irrigation was set up for the new plantings, and then things were left alone.
Within one year, with nothing else done to those areas, a minimum of one inch of topsoil had been restored to those mulched beds.
At 18 months, the shady corner of the yard that had been mulched first to a depth of 3 inches with hardwood chips had topsoil fully three inches deep. And only one inch of wood chips left.
Geez, that was easy. So who did the work?
Insects, birds, microorganisms and earthworms carried the load. Even if you don't care about birds and butterflies, but just want some pretty flowers, mulching the soil is the single most effective thing you can do to earn yourself some fluffy dirt. Mulch retains moisture and is insect, earthworm and microorganism habitat. Birds contribute the least--a little nitrogen and a little aeration. Its the little guys that really work like trojans to break down the organic pieces we give them and turn them into garden gold.
Are some types of mulch better than others? In my opinion, yes. Landscape fabric can be necessary to protect a structure, and may be an advantage up next to the house. But the bugs can't eat it, and that keeps them from getting to the actual mulch. So stick with newspaper or cardboard as your underlayment. I know you're thinking-- "why would I want them to eat my mulch?" Because increasing the organic matter in the soil and allowing those little guys to open up new tunnels for air, roots and water to travel through will make your plants happy without fertilizer, making for stronger, more disease-resistant plants. After all, it's really not that hard to add a new layer of mulch as needed.
As to which of the options you have for the "real" mulch (not the newspapers)--start with what nature gives you. Fallen leaves and pine needles are ideal. Pine bark is another good one. Shredded hardwood can also be good--try to stay away from dyed versions. Some hardwood mulches harbor a type of fungus which can "explode" onto your house/car--and stick there permanently. It's not easily visible, so if you're at all nervous about the possibility, either don't use hardwood mulch or use it on beds away from your house and driveway.
I haven't even touched on compost yet, but I'll leave that for another day. Happy mulching!
[Photo middle: starting something great. Bottom right: have fun with your mulch!]