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Mulch

Mulch is used as a cover to protect and nourish soil. Organic materials are usually used as mulch, although inorganic materials such as pebbles can be used. Bare soil rarely occurs in nature, and in most cases it is best avoided in the garden.

The depth of mulch can vary, from a light sprinkle between seedlings, to a no-dig garden with 15cm or more of deep mulch which is used as a growing medium.

Benefits of mulch

Reduced water evaporation arising from protection of soil from the drying effects of wind and sun.
Addition of organic matter and nutrients, improving fertility, structure and water retention.
Increased biological activity within the soil.
Maintains soil surface condition, eliminating problems of crusting and assisting with non-wetting soil.
Eliminates dirt splash, a problem that can create diseases in plants.
Reduces weeds by smothering and limiting germination. Invasive weeds can be easier to manage.
Harbours beneficial predators such as spiders and centipedes.
Reduces erosion by slowing the movement of surface water.
Buffers extremes of soil temperature.

Problems associated with mulch

In dry weather, water can be prevented from reaching soil.
Harbours pests such as slugs, snails and earwigs.
Soil warming is slower in Spring.
Fine thick mulch can block air from entering the soil.
Some weeds, with a mass of fibrous roots, can be difficult to remove without losing lots of mulch.

Some mulch materials

Organic gardeners see organic matter as a resource to be gathered rather than as a waste product. There are many different kinds of materials that can be collected for using as mulch. Look aroung to find what is locally available.

Straw and hay
Any straw or hay is suitable for vegetable and flower gardens. Avoid material with weed seeds. Shake the hay before adding it to the garden if you suspect it contains seeds. Lucerne hay is the best mulch material as it contains a good range of essential elements. Pea straw has reasonable nitrogen content but is very light and breaks down quickly.

Bark/woodchip/sawdust
These woody materials form a long term attractive cover, especially suitable for landscaping and ornamental gardens. Sawdust is good on pathways.

Leaves
Large leaves should be shredded or mixed with other materials before being used as mulch or they will form a matted waterproof layer. Some leaves, such as eucalypt, walnut and pine (acidic), have an adverse affect on soil life. Leaf mould, made by allowing a pile of leaves to completely decompose, is a good mulch and a good soil conditioner.

Shredded branches
An excellent coarse mixture of wood chip and leaf. Home shredders can turn prunings into mulch. Large quantities may be purchased from garden supply depots. Avoid eucalypt, olive (which may contain seeds) or pine based shredded mulch.

Newspaper
Use under other materials to smother weeds. Do not leave paper uncovered or it will get blown about and create a mess. Glossy coloured paper is toxic and must not be used.

Seagrass
Long lasting cover which breaks down very slowly. Collect after rain to avoid salt or water it down before applying. Check with Council for permission before collecting. The last time I asked it was allowed to gather seagrass by hand, provided vehicles were not brought onto the beach.

Lawn Clippings
Do not apply lawn clippings too thickly or they will go slimy. They do not last long and break down quickly. They may contain couch or kikuyu pieces, which can regrow. The properties of a lawn clipping mulch depend upon the type of lawn. Clover provides a higher nitrogen content, whereas kikuyu is fibrous, with a higher proportion of carbon. Lawn clippings are very fine. They are best used on top of other, more open, mulch materials.

Weeds
Provided they are harvested before seed set, weeds make an excellent mulch. Invasive weeds which might regrow should be dried out before being used as mulch.

Old Garden Plants
When you take out those old vegetable plants, you can chop them with a spade a couple of times then leave them in the garden as mulch. Keep in mind the need to avoid spreading plant diseases - tomatoes for example should be composted..

Poultry litter - Any of the materials listed above may be left in a chook yard for a while before using as mulch. Chooks will clean out weed seeds and add manure to the mulch.

Manures - Do not apply raw manures directly to the soil unless they are mixed with and covered by a large bulk of other mulch materials. Failure to follow this rule will result in an unhealthy offensive garden environment.

Non-organic mulches
The use of plastic as mulch is not recommended. Plastic will not break down and will become a nuisance later. Although plastic, used with other materials, provides an effective weed smother, many invasive and persistent weeds grow through the plastic, which obstructs the gardener when trying to clear these weeds.

Small stones, gravel or pebbles are an attractive mulch. They provide many of the advantages of an organic mulch, without the benefits of improving soil fertility. Water penetrates quickly through It can be tricky using garden tools to weed through gravel. When planting trees for revegetation work, you can put around each tree a mulch of stones or small rocks.