The aerobically decomposed remnants of organic matter used to enrich soil.
Peat-free composts commonly consist of composted bark, wood fibre and coir, with added nutrients. Using peat-free composts has considerable environmental benefits for peatlands, which are now threatened habitats.
Loam-based composts from the John Innes range, are soil based, rather than peat based, with good moisture and nutrient-retentive qualities.
Additional soil conditioners include vermiculite and perlite. Vermiculite is a mineral that forms spongy, lightweight kernels that enable the soil to hold more water. They're also useful in preventing the compaction of soil and in loosening heavy soil. It's also used as a medium in which to root cuttings. Perlite is a lightweight aggregate made from an amorphous volcanic or other vitreous rock. Totally inert and sterile, it's useful in opening cavities in the soil and enabling water and air to reach roots. It's often used in potting soil.