There are many reasons to use mulch and many kinds of mulch from which to choose. The mulch you select should be related to the purpose(s) you have in mind so identifying the reason you are mulching is important in finding the one that suits you and your garden best. Most people hope to accomplish several goals with mulch but other considerations such as cost and appearance come into play and also influence the selection process.
So, why mulch? Here are the reasons I apply mulch to my garden.
1. Suppression of weeds: mulch can reduce germination and growth of weed seeds and seedlings. But some mulch inadvertently adds weed seeds.
2. Conservation of water: mulch reduces the evaporation of water from the soil and can aid in preventing the formation of a crust on the soil that will keep water from entering.
3. Addition of organic matter and nutrients: as some mulches decay they release organic matter and nutrients into the soil. Some mulch adds nutrients, but others actually take nitrogen out of the soil during the decay process.
4. Prevention of erosion: by reducing the force of heavy rains, less soil is washed away.
5. Modification of temperature: in the summer mulch can shade the roots from the heat of the sun while in the winter it acts as insulation against freezing temperatures. (In spring, however, the mulch may hinder the warming of the soil.)
6. Appearance: some mulch is very attractive and can add color, texture, and uniformity to the garden.
Some reasons are more important right now, others will be so later in the year. For example, in the winter I want my plants to be protected from extremes of temperatures, but in the spring weed suppression is a biggy; in summer, moisture conservation is the primary concern. And through out the season I want the garden to look nice so shredded newspaper is not going to cut it (pardon the pun). Then too, there are personal preferences; I just don’t like red brick chips.
There are basically two categories of mulch, organic and inorganic. Organic mulch come from plants. It breaks down and thereby changes the soil characteristics while most inorganic mulches such as stone or landscape fabric do not break down and so will not change the soil characteristics. Because they breakdown, organic mulches have to be replaced regularly. Some, like grass clippings, break down very quickly and may have to be renewed many times times during the growing season, others like bark chips decompose slowly and may last the whole summer, depending on your climate. Inorganic mulches breakdown slowly if at all and generally do not have to be replaced so often. They add no nutrients or organic matter to the soil.
Here is a list of common, available mulches with their major advantages or disadvantages. There are many locally available mulch materials like coconut shells that may be just as useful but their availability is a limiting factor and I have not included them.
Compost: may contain weed seeds and carry disease; some compaction may occur, but high in nutrients and organic matter.
Bark Chips: decomposes slowly.
Wood Chips: decomposes slowly; very much like bark chips.
Shredded bark: excellent but may decay more quickly than bark chips or wood chips.
Manure (well rotted): direct from the stable may contain toadstools, other fungi, disease bearing material, and weed seeds; sterilized and bagged manure should be free of contaminants; may decompose more quickly than bark chips, wood chips, or shredded bark.
Grass clippings: free; may contain weed seeds; decomposes quickly; prone to compaction.
Sawdust: blows when dry, cakes after being wet.
Straw: may contain weed seeds.
Peatmoss: may blow; difficult to wet when dry.
Paper: cheap but very unsightly; blows around unless wet; easily mats.
Leaves: tend to compact; composted leaves are much better.
Pine Straw: inexpensive, easy to distribute, decomposes slowly but gets shabby looking.
Wood Shavings: tendency to mat; nitrogen fertilizer should be added so nitrogen is not leached out of the soil.
Plastic Film (clear or dark): not attractive; most valuable for warming up soil in spring; black good for preventing weed seed germination.
Geotextile: good for suppression of weeds; use with decorative mulch.
Solid Rock (like pea gravel or river rock): decorative; use with plastic
Crushed Rock, Gravel: use with plastic.
For my garden I am partial to the wood chips, bark chips, and shredded bark because they add nutrients and organic matter to my clay soil and look relatively neat and attractive. When I apply them in the spring they last through the summer and fall, and decompose by spring in time for the soil to warm up. I use compost as a soil additive rather than as a mulch, mixing it into the soil before applying mulch. The head gardener uses a huge amount of pine straw around the trees and shrubs in our “woodsy” areas because it is cheap and easy to apply but I consider it is a too coarse and rough looking for my garden beds. In a different climate my mulch materials of choice might be very different.