Organic mulches are ideal for vegetable gardens because they decompose and add nutrients to the soil while they suppress weeds and hold in soil moisture. Use mulch that does not contain harmful chemicals or dyes, especially around food crops. Rather than purchasing exotic mulches and finding them unavailable when you need to touch up the garden, use materials that are available locally or free from your own yard.
Using fallen leaves as mulch is a handy way to dispose of leaves in the autumn. Leaves should be shredded so they don't layer and clump together, possibly harboring mold and fungi. Shredding also helps them decompose faster, and makes them lighter and easier to spread. Shredded, dried leaves such as oak, which are acidic when green, will not alter the soil pH of your garden. The acidity is lost when the leaves die and turn brown.
Hay, Grass and Straw
Hay, grass and straw are similar mulching materials, but there are differences in their effectiveness. Hay is dried grass that was cut in a green, growing state; it includes seed heads that can populate your garden as weeds. For this reason, hay is not an ideal mulch.
Fresh green grass clippings from the lawnmower are already chopped into fine bits and ready to be used as mulch. They contain moisture, which can cause high temperatures within the decomposing layer of mulch; it is a good idea to allow grass clippings to dry before applying them as mulch.
Straw is the brown plant that remains after the harvest. Straw decomposes slowly and is easy to handle. It gives the garden a clean look when it is used between rows or planting beds. Grass or straw are ideal to layer over garden walkways. They form a mat that helps minimize soil compaction from footsteps.
Two kinds of living mulch can be used in a garden. The first is simple shading, which occurs when the plants are set close enough together so their mature leaves meet and form a canopy over the soil. The shade effect limits weed growth and reduces evaporation from the soil.
The second kind of living mulch is a cover crop that is planted between rows or beds, or over the entire garden in the fall. The cover crop seeds are sown densely to choke out weeds. Living mulch cover crops are tilled under before they mature to improve the soil tilth and fertility. Buckwheat and oats are examples of living mulches.
Newspaper makes good garden mulch. Check with the newspaper's printer to make sure the ink is soy or vegetable-based; synthetic chemical inks are toxic and should not be used as mulch. Newspaper sheets can simply be laid out in the garden in a layer four sheets thick. Spray the layered newspaper with water and spread a light layer of another mulch over it to keep it in place.
An alternative way to use newspaper as mulch is to shred it first, then apply it as you would any other shredded mulch. Shredded newspaper can be mixed with other materials like shredded leaves or straw. An additional benefit to using newspaper mulch is that earthworms are attracted to it.
Mulches to Avoid
Shredded wood, wood chips, sawdust and bark mulches may seem attractive, but they are not necessarily good for your garden. They require a high concentration of nitrogen for their slow decomposition process, and they pull the nitrogen they need from the very soil your garden plants are growing in. Wood-product mulches can actually starve your garden plants and upset the pH balance of the soil. Shredded wood mulch is made from all kinds of scrap wood, pallets and treated wood that contains any number of toxic chemicals. "Shotgun fungus" also grows in wood mulch, which creates permanent stains on surfaces.
Rubber mulch is made from old tires. Tire rubber is hardened by bonding processes that use toxic chemicals. After being shredded for mulch, the rubber breaks down and releases the poisons into the soil. Rubber mulch gives off a foul odor in summer heat. Rubber mulch should never be used around food crops.