Organic mulches last one to three seasons and then must be replaced. Some types of organic mulch form a crust that inhibits water percolation. Periodically rake the mulch to break up any crust that has formed. Remove or incorporate decayed organic mulch into the soil before adding more mulch. Organic mulches include straw, leaves, manure, pine needles, leaf clippings, shredded bark, wood chips, sawdust, compost, composted sewage sludge, etc.
Inorganic mulches provide a long-term ground cover.
A weed-control mat should be placed below the mulch. Use a mat that allows water to penetrate. Marble chips, river gravel and crushed brick are popular inorganic mulches. Weed control is important for water conservation. Weeds will compete with desired plants for water and nutrients.