Applying mulch is the best time-saving measure a gardener can take. This is true for every type of garden—flower beds, vegetable gardens, hardwoods. When you mulch a garden it is healthier, has less weeds, and the mulch helps hold moisture so the garden is more drought resistant and you spend less time watering.
Organic Gardening offers the following advice:
There are two cardinal rules for using organic mulches to combat weeds. First, be sure to lay the mulch down on soil that is already weeded, and second, lay down a thick enough layer to discourage new weeds from coming up through it. It can take a 4- to 6-inch layer of mulch to completely discourage weeds, although a 2- to 3-inch layer is usually enough in shady spots where weeds aren’t as troublesome as they are in full sun.
Organic mulches include formerly living material such as chopped leaves, straw, grass clippings, compost, wood chips, shredded bark, sawdust, pine needles, and even paper. Inorganic mulches include gravel, stones, black plastic, and geotextiles (landscape fabrics).
Organic mulch will decompose and have to be replaced, however in the process it will also improve your soil.
Bark and chipped wood mulches, which are best to use around trees and shrubs where you won’t be doing a lot of digging, can cause problems. Tree trimming services and county chip piles may be inexpensive or free, but stop and think for a moment…most tree removal is a result of disease. Some winters, like this last one, will create a lot of debris for chipping. Best advice is to know your source.
Mulching around trees is intended to protect it from mechanical damage from weed whackers and lawn mowers, reduce weeds, and hold moisture. If the mulch is piled up the truck so the skirt of the trunk is hidden, it obviously isn’t holding moisture where needed—all the way out to the drip line at the end of the branches.
Chipped mulch has its problems, and so does cocoa mulch; it contains a lethal ingredient called Theobromine which is the ingredient used to make all chocolate—especially dark or baker’s chocolate. This ingredient—and so the mulch—is toxic to dogs and cats. Of course it smells like chocolate so it is especially attractive to dogs (and small children). A pet will ingest this stuff, become horribly sick, and possibly die. My advice, choose something else.
My mulch of choice is natural cypress, straw, and leaf mulch (from a reliable source!). They all breakdown and, like compost, improve the quality of the soil.
(Photo of improper mulch in volcano stack from Tom LeRoy, http://www.gardeningwithtomleroy.com/175)