Mulch is anything that covers the soil for the purpose of preventing weeds, conserving moisture, or moderating the soil temperature. Many materials make good mulch. The ones you choose really depend on what's locally available, how much you want to spend, the appearance factor and where you plan to put it.

The best mulch materials for gardens and landscapes also feed the worms and add organic matter to the soil as they decompose. Usually, 2- to 4-inch layers are sufficient to do the job, depending on the density of the material. Take a look at the following popular mulches and their uses.

Tree bark: The ubiquitous landscape mulch. Available in shreds or various-sized chunks, bark lasts a long time, depending on the particle size and gives your landscape a finished look. Be sure you're buying real bark, however, by checking the bag label or asking the seller for the content. Wood chips that are dyed to look like bark are becoming prevalent in some areas.

Wood chips, sawdust and shavings: Although suitable for mulch, these products break down more quickly than bark and compete with your plants for nitrogen as they decompose. If you use these around food and landscape plants, be sure to add an additional nitrogen source such as animal manure or cottonseed meal. Never use materials from chemical- or pressure-treated wood.

Shredded leaves and pine needles: These are among the best sources of free, attractive and nutrient-rich mulch for flowerbeds, fruits and vegetables. Be sure to shred leaves before using to prevent matting in the garden. In fact, it is best to run over fallen leaves with a lawn mower, discharging them into easy-to-rake mounds.

Seed hulls and crop residue: These attractive, locally available, lightweight materials include cocoa bean, buckwheat hulls, ground corncobs and other materials left over from processing an agricultural crop. Use on top of newspaper or other sheet mulch to increase suppression of weeds.

Straw and hay: While these are traditional vegetable garden and strawberry mulches, beware! Hay contains weed seeds that will add to your problems. Straw from grain crops, such as oats and wheat, may contain some crop seeds, but is a better choice as weed-suppressing mulch. Allow the soil to warm up in the spring before putting mulch around tomatoes and other heat-loving crops because straw keeps the soil cool.

Law clippings: Clippings cost nothing and work best in flower and vegetable beds where they decompose quickly. Allow the clippings to dry on the lawn and then rake them up before using. Fresh clippings may mat down and become slimy as they decompose.

Newspaper and cardboard: Use cardboard or several layers of whole newspaper sheets in pathways or around landscape plants to smother weeds. Avoid the colored glossy pages. Cover with a thick layer or loose mulch, such as bark, shredded leaves or straw. Depending on rainfall, you may have to replace newspaper during the growing season.