Sustainable Gardening

MULCH

Not all compost has to be made in a bin or even by piling the makings up somewhere. Some of the best and most nutritious composts are those made right where they are going to be used, by the method known as sheet composting or sheet mulching. This is after all what nature mostly does since she is unable to gather waste into neat piles without human help.
  ~ Moira Ryan - Organic Gardener, Author &   Professional Botanist - Zone 9, New Zealand


Mulch/Sheet Composting/Sheet Mulching
 16 important benefits/reasons for use:
 

■ Enhances soil structure and overall health

■ Increases water infiltration into the soil

■ Improves nutrient and water retention

■ Saves water: Saves up to 73% of water     loss through evaporation

■ Suppresses weed growth

■ Suppresses pathogens and pests

■ Prevents soil compaction

■ Provides a source of organic matter for the     Soil Food Web

■ Increases healthy Soil Food Web: Soil     microbial activity and worms

■ Improves plant vigor and health, which     improves resistance to pests and diseases

■ Turns the soil into a living filter which     removes pollutants from water, protecting     our waterways

■ Helps moderate and maintain balanced soil
    temperatures: Cooler in summer and helps
    protect from freezes

■ Controls erosion

■ Reduces need for pesticides, herbicides,
    and fertilizers

■ Reduces waste: Composting and mulching     green waste conserves dwindling landfill     area. reducing greenhouses gases and air
    pollution from transport

■ Reduces labor and maintenance costs:     weeds are composted in place and the     repeated use of chemicals are not needed

 

Mulch should never be applied to dry ground, as often this can cause it to become an impervious roof and shed water instead of allowing it to soak in, resulting in the mulch not providing its wonderful benefits.

 

It is not advisable to dig wood mulches into the soil. Mulch is best used as nature intended, applied to the surface where the soil organisms can draw on them as they are needed, and meanwhile they can act as good insulators, weed suppressers and moisture retainers, etc. As long as mulch is spread on the soil surface only, it is highly unlikely to rot quickly enough to cause nitrogen robbery of the topsoil. Left strictly alone, the fungi and bacteria will get the nitrogen out of the air to digest pure wood. Dig that stuff under and they will take it from the soil and there will not be any nitrogen available for the plants. Nitrogen deficient plants turn yellow and become weak and susceptible to pests and diseases.

(Nature's mechanism is geared to receiving raw materials at the surface and so the most efficient breakdown occurs in mulches and not in material dug into the ground, but the notion of digging stuff in has become so deeply entrenched that many people feel unhappy about tending a garden without any digging.)


 

Mulch/Sheet Composting/Sheet Mulching
 
The sheet compost/mulch system applies layers over soil, with mulch on top.

*For difficult weeds - see Weed Control.

1. The soil must be wet before you start -all
  layers must be wet, or the layers will not bond with   the soil and you will not get the results you want.
2. If the area has a few weeds or thick grass,
  cut down or mow grass or flatten weeds and leave
  in place (remove if has weed seeds).
3. Apply weed barrier - a layer of sections of or   whole newspapers (wet until almost pulpy in 5 gal.   bucket) and cover soil 1 in. thick. (overlap sections   by several inches) Keep wet.
  (don't use the shiny advertising sections)
4. Apply a thin layer of moist weed-free compost   or wormcastings 1/2 inch thick. Wet down
  well.
5. Apply 4-6 inches of wood chips, shredded
  wood, or a mixture that may also include some   leaves.   This layer mimics the newly fallen organic
  matter of the forest.
6. Wet complete area well and do not let dry out.

* If the area is mostly weed free the newspaper
   layer can be skipped.
* In the hot central valley, cardboard without the    newspaper layer first will usually not bond with the    soil due to our extreme temperatures.
* The top mulch layer will need to be replaced in 6-12    months, depending on materials used, etc.

Soil fertility and mulch: The faster your mulch disappears on the soil the more fertile your soil is. If you have extremely fertile soil, you may want to have a form of nitrogen available between soil and mulch. for example: weeds, grass clippings, etc.

 

Wood Chips are not born equal. 
Those from ramiel wood (young growing wood below 3 inches diameter) have a preponderance of sapwood. This is wood in an immature state still containing many live cells and hence plenty of nitrogen of its own. Wood in this state, especially if applied where there are at least some woody plants growing, usually rots down with the greatest of ease especially if it is shredded finely.

 

Chips from mature wood are most likely to consist largely of heartwood which is quite dead and consequently has virtually no contained nitrogen remaining. Quite often, especially in conifers, it is further protected from rot by storage of resins and similar inclusions.


* If you want to add living material on top of your existing soil or ontop the newspaper/cardboard layer, add a layer (about an inch) of compost or worm castings. Do not dig it into the soil. A high quality compost or worm castings can change the biology of the soil and in time you should have healthy soil that will support and nurture your plants. Even hard compacted soil will be changed over time, as long as the next step, which is to mulch is also followed.


To plant: Push back the mulch and cut a hole in the newspaper/cardboard layer and plant plants in the soil, replacing the sheet mulch layers. Smaller plants can often be planted right into the top mulch/compost layer. A small amount of compost may need to be added around the rootball if the compost layer had not been included before the top layer. Remember to keep mulch several inches away from woody stems and from tree trunks, so as not to invite rotting and disease to the cell wall.