Okay, now that we have a basic understanding of what compost is and what mulch is, let’s make the differences a bit clearer.
Compost is mixed into the soil; whereas, mulch is spread on top of the soil.
Compost is best at adding nutrients to the soil and “improving” soil structure.
Mulch is best at limiting weed growth, preventing erosion and retaining soil moisture.
Compost is made up of decomposed, organic materials; whereas, mulch can be inorganic (think ornamental rocks or ground rubber chips) or organic materials like wood, that, in most cases, are not decomposed.
Compost is usually a rich dark color of deep brown to black, and no colorants are added. Mulch, however, can be dyed with various colorants in big machines to make it black, brown, golden or even red. Dying is more expensive and will cost more.