Mulch is a blanket for your soil; a layer of it applied to the soil surface promotes healthy plants and earth. A spring application of mulch is a great way to prepare your garden for the growing season.

Before deciding what works best in your garden, consider the different types of mulch. There are two categories: inorganic and organic. Inorganic mulch, such as gravel or rocks, helps keep weeds at bay, lasts longer and can offer a manicured look.

Organic mulches include bark nuggets, shredded bark, arborist chips (sold in bags as "play chips") and compost. Bark nuggets and shredded bark, which are useful for garden paths, tend to shed water (the role of bark on the tree). This could work against you when used as mulch for the garden because bark can form a barrier that prevents water from filtering through.

In most climates, organic mulches, such as compost and wood chips, are a preferred top-dressing for planting beds because they enrich the soil when they decompose. Other practical benefits of mulching include:

Suppress weeds. Even if weed seeds blow in and germinate, they'll be easy to pull up from loose material such as compost mulch. Some gardeners use 1 inch of compost with 2 inches of arborist wood chips on top for extra weed control.
Improve soil. Compost mulch provides some nutrients to the earth as it breaks down and helps with soil structure. Compost mulch used on clay soil year after year will eventually help break up that heavy texture. Conserve water. Compost mulch won't let your soil get too soggy or dry. Instead, its texture helps moderate the flow of water, so a soaking from the sprinkler or a heavy rain filters through slowly instead of running off and decreasing evaporation.
Reduce erosion. Exposed soil gets washed away in the rain and blown away in dry weather; the top of the soil develops a crust that prevents water from penetrating. Compost mulch slows the water and protects the soil.
 

How much mulch do you need? Two inches of compost mulch can be applied yearly.

There are a couple of cautions when using any type of mulch. Apply no more than 3 inches, and keep it thin around shallow-rooted plants such as rhododendrons, azaleas, magnolias and peonies. Don’t pile mulch against the trunk of trees or shrubs. Instead, keep it a few inches away to prevent moisture buildup that can lead to trunk rot.