A mulch is basically a material you spread over your soil that keeps heat in and frost out and helps your soil develop.
However, there are many different types of mulch. From inorganic material that just keeps the frost out of your soil to organic mulches that break down and act like compost.
Inorganic mulches include non-rotting materials like stone, plastic granules, gravel or rubber particles/chippings.
These are useful at keeping out frost, reducing weeds and keeping the moisture in the soil.
However, they are not as useful as organic mulches in that they don't decay, break down and provide nutrients and can lead to the prevention of moisture entering the soil and over-heating of the soil.
Organic mulches include grass clippings, leaves, wood chips, bark, coffee beans, hay, straw or even your own composts.
These are useful for all the same reasons as inorganic mulches, with the additional benefit of breaking down and providing nutrients and encouraging useful worms, insects, bacteria and other life that can thrive, control pests and benefit the soil.
They insulate the soil, keeping it warm in the wider months but cooler in the summer months and aid the soils moisture absorption. They can also stop the soil from clumping into hard patches, so helping seeds take and grow and helping water penetrate the soil.
N.B. All mulches pictured in this article are organic, (wood chippings and bark types)