Glossary of terms

Activator - added to raw materials to speed up the composting process. This is usually in the form of additional nitrogen (either chemical fertilizer or organic).

Additives - materials used to improve the chemical composition, physical structure, supply micro-organisms, or reduce nitrogen losses in a compost heap.

Aerobic - in the presence of air or oxygen.

Amendments - a material or component added to a growing media to improve its physical or chemical characteristics. Generally does not exceed 10% of the entire mass.

Ammoniation - the lowering of a C/N ratio through the process of adding a source of nitrogen (ammonia, urea, etc.) to a material with which is difficult to decompose quickly (one with a high C/N ratio).

Anaerobic - in the absence of air or oxygen.

Bagasse - the plant residue remaining after the extraction of juices from sugarcane.

Bulk Density - a ratio of the dried weight to its unit volume of material (g/cc).

Carbon/Nitrogen Ratio (C/N) - the ratio of carbon to nitrogen by weight in an organic material. This is an important value when composting.

CEC (Cation Exchange Capacity) - the sum of the exchangeable cations, measured in units called milliequivalent, that a material can adsorb per unit weight or volume - the larger the number, the greater the nutrientholding ability.

Components - the ingredients or materials which comprise a growing media. A component is usually at least 10% of the media.

Humus - complex and stable organic matter resulting from the decomposition of plant and animal material.

Hydrophilic - material which attracts water.

Inoculant - microorganisms (bacteria, fungi, etc.) added to a compost heap in order to promote composting.

Macropores - large air-filled pores in material from which water can drain freely and serves to aerate.

Marc - the residue remaining after a fruit has been pressed.

Mature - when composting material has broken down completely to form humus.

Mesophilic - the lower temperature stage in composting prior to and after the thermophilic stage) during which less active decomposition occurs.

Micropores - the small pores in a media which hold water after gravity has drained excess water from macropores

Organic Fraction - the portion of a media (or soil) consisting of organic material.

Phytotoxic - that which is poisonous to plants.

Pomace - the dry or pulpy residue of material from which a liquid (as juice or oil) has been pressed or extracted.

Porosity - the percent of total volume not filled with solid particles.

Potting Mixture/Media - used interchangeably with growing media to describe the artificial soils used in container nursery culture.

Substrate - any media used in containers in which plants are grown.

Thermophilic - the stage in composting during which high temperatures (45-70 °C) are reached. This stage is necessary for killing pathogens and weed seeds in compost.

Wetting Agents - added to a media to increase the ability to absorb water. Often added when components are hydrophilic.