A mulch can be any kind of material that can be put onto the soil with injuring the plants that you want. What is important is not so much the material that you are using, as what you are using it for. As such, even a sheet of plastic can work. The key advantage of decomposable mulches is that over the long term they can add benefits to the soil itself.
While the chief benefits of mulching are considered to be water retention and weed suppression, other benefits exist as well. These are as follows:
- Water Retention - When properly applied, water loss due to evaporation is reduced. As a consequence, less watering is needed. Particularly useful in areas prone to droughts.
- Weed Suppression - Except where openings have been provided seed germination is suppressed, and any seedlings that do sprout are typically smothered by the layer of mulch. Just make sure that your choice of mulch does not include weed seeds of its own.
- Insulation - It has been experimentally shown that a two inch layer of mulch can reduce soil temperature extremes by as much as 30 degrees fahrenheit. The result is the roots systems are less susceptible to damage from either frost or drought.
Any number of materials may be used, but here are some common choices along with considerations for use.
- Buckwheat Hulls
- Cocoa Shells
- Elm Leaves - Tends to raise ph levels
- Grass Clippings - should be used as part of a mix rather than alone.
- Hay or Straw -needs at least an 8 inch layer to be effective. More suitable for orchards than for gardens.
- Maple Leaves - Tends to raise ph levels
- Newspapers - uses more nitrogen in the first year of application than it releases. Consequently, either mix with other materials or add nitrogen fertilizer prior to application.
- Oak Leaves - Tends to lower ph levels
- Peat - Tends to lower ph levels
- Peanut shells
- Pine Needles - Tends to lower ph levels
- Oak leaves - Tends to lower ph levels
- Sawdust - sames as for newspapers.
Note that mulches that affect ph levels can be either negative or positive depending on what you are trying to grow. Example: Azaleas benefit from mulches that lower ph, but are hindered by those that raise it.