Keeping the layer deep enough to do the job is important, too. This means you will need to add more mulching material over the old layers to get all the benefits of mulching. Mulching with grass clippings is a good way to dispose of the clippings, but don't use more at one time than will dry readily. Sawdust makes a better mulch if it is well rotted, or if you add one cup of ammonium sulfate or calcium nitrate to each cubic foot of fresh sawdust before applying the mulch. Weed-free straw is excellent, but loose straw can be a fire hazard, and some people consider it unsightly.
Mulches suppress weeds, thus saving a lot of work.
An occasional weed may poke through the mulch, but you can easily pull it out. Mulches can be used to regulate soil temperature. Many plants, including those in vegetable and flower gardens, need a cool surface soil. Others, such as tomatoes and vine crops, may benefit from warmer soils. Organic mulches condition the soil and furnish food for earthworms, which are valuable in aerating the soil.