Almost any material that is organic (can decompose over time) can be used as mulch or worked into the soil to feed the earthworms and soil microbes. Ideally we would like to have a supply of organic material that is free. Here are a number of additional options for organic soil amendments.
Shredded newspapers, junk mail, or computer printouts make perfectly good organic soil amendments as long as they are used in concert with some other material such as wood chips or peat moss. Shredded paper as a mulch has the one disadvantage of turning into paper mache after a good rain unless it is mixed with some other material that prevents it from binding together when it is wet. Shredded paper mixed with wood chips or peat moss doesn’t look terribly wonderful as a mulch, but when covered by a thin layer of shredded bark, no one knows the difference and the earthworms are happy.
If you till shredded paper into the soil as you prepare a bed, there is no need to add any other materials, although some peat moss would not hurt.
While grass clippings are best left on the lawn to add nitrogen and organic matter to turf soil, there are some times when grass gets so long that you must collect the clippings or they will clump on the turf. Use them as mulch. Spread them in thin layers--no more than an inch thick--so that the air can dry them before they decay and become putrid. Because grass clippings break down and disappear quite quickly, use them in conjunction with an existing mulch of chopped leaves, rather than as the sole mulch, to prolong their usefulness.
Never use grass clippings that have herbicide residue on them which may harm tender ornamental plants. Grass clippings that have been soaked by at least 1/4 inch of good rainfall after being sprayed with herbicide are usually free of any dangerous levels of the chemicals.
If you live near a manufacturing operation that produces piles of sawdust, you have a source of perfectly good organic soil amendment but you need to be very very sure that the sawdust has been sitting outside in the rain for at least a year. If you use fresh sawdust, it will pull nitrogen needed by your plants from the soil as it decomposes quickly. Aged sawdust dug into the soil or used as a 2 to 3 inch layer of mulch makes a happy soil over the years.
Stone or Rocks Not Desirable
Some folks with a good supply of rocks and stones will sometimes use them as mulch around trees and shrubs. While stones may keep the weeds down, they give nothing to the soil in terms of organic food for the earthworms and soil microbes. We don’t recommend stone as a mulch.