What is mulch? Mulch is a material that is spread around a plant or over the soil surface as a protective layer. If we think of soil as a ‘cake,’ the mulch is simply the ‘icing’ or ‘topping’ that provides a huge range of benefits for you and your garden. Mulch comes from a wide variety of organic or inorganic materials and ranges in cost from free to expensive. Why do you need it anyway? These are some of the reasons to use the ‘marvellous miracle of mulch’ in your garden: 1.