Mulch is a layer of either organic or inorganic material that is placed as a soil cover around landscape and garden plants. Mulch benefits the landscape by not only helping with soil moisture retention and weed reduction, it also helps reduce soil surface temperatures and enhances the aesthetics of the landscape.
Inorganic mulches include gravel or rocks, etc., which are available in a range of sizes, colors and shapes. Some plants, particularly those that cannot tolerate excess moisture near their crowns (such as Penstemon, Eriogonum and Cacti), require gravel mulch because it does not retain moisture at the soil surface like organic mulch.
Organic mulches can include shredded wood or bark, grass clippings, shredded leaves, sawdust, newspaper, etc. Organic mulches can improve the soil as they biodegrade, however, those that decompose rapidly can also rob plant material of nitrogen. Nitrogen is mobile within plants. When nitrogen is in short supply it is moved from older foliage to new foliage as needed, therefore nitrogen deficiency is first noticed as a yellowing in a plant’s oldest foliage. When incorporating organics to the soil, additional nitrogen should be added to meet both the needs of the plant and the decomposing organic matter. The amount of nitrogen needed will depend on your soil, the plant itself, the type of mulch and the quantity used. Too much nitrogen at once can burn plants, so use a slow release type and add in light doses. (See the fertilizing article for information on fertilization)
When applying mulch, it can be spread directly on the soil surface or over a weed barrier fabric. Weed barrier fabrics are more desirable when using inorganic mulches to keep the soil and rocks separate. If you choose to use a weed barrier fabric, use a product that allows water to percolate through the barrier into the soil and plant roots below; DO NOT use plastic! The depth of mulch should be 1 to 3 inches for perennials and annuals, and 3 to 4 inches for shrubs and trees. However, keep the mulch pulled back an inch or two from the base of woody shrubs or trees.
There are many sources for purchasing mulch. The right choice depends on your landscape, its plants and your personal taste in product type and color, and budget. Most Garden Centers offer a variety of products to choose from, which can be purchased in bulk or by the bag.
Consider your local landfill when looking for a sustainable source of landscape mulch. Many landfills now have recycling programs that are entirely separate from their other focus. Their products can be a good, cheap, sustainable source for mulch. If you’re unsure, ask about their process.
The Wasatch Integrated Waste Management Facility in Layton sells compost and mulch products http://www.wiwmd.org/PDF/GWR%20Brochure.pdf
In the past, it was often felt that Cedar Mulch was preferable because it had natural oils that helped repel insects. However, as the demand for Cedar mulch has increased, the trees used to make cedar mulch are younger and younger and may no longer perform these repellant properties