Organic Growing Media: Constituents and Properties

Abstract

Organic growing media are essentially bulk products. Availability in large quantity allied to its excellent air and water retention, low pH and salinity, and freedom from pests and diseases has led to peat being the dominant organic constituent of growing media in many parts of the world for the last 50 yr. The unique microporous properties of Sphagnum peat and its resistance to degradation are matched by few other growing media constituents. Nevertheless, local scarcity of Sphagnum peat and the expense of transport has led to the use of other materials in growing media. Notable among these is coir, which unlike peat, a CO2 sink, is widely regarded as a rapidly renewable resource. Indeed, advances in processing and quality control in situ have led to a huge upsurge in the export and use of coir in growing media, particularly in Europe but also in the western United States. Locally available organic materials such as bark, composted materials including green (yard) wastes, municipal solid wastes, and even sewage sludge are also used in growing media. While possessing advantages such as the high air content of bark and nutrient supply of many composted materials, these media components may have disadvantages, from limited supplies due to bioenergy pulls and N lock‐up in bark, to physical, chemical, and microbial contaminants in composts. Current innovative approaches involve increasing use of wood fiber in Europe, whole pine‐tree thinnings in the United States, and realizing the use and transformation of composted wastes as next‐generation constituents of growing media.

Increasing Sustainability of Growing Media Constituents and Stand-Alone Substrates in Soilless Culture Systems

“…Therefore, according to Massa et al [87], efforts should involve the adaptation of new technologies for tracking raw materials and supporting sustainable circular chains for compost production at a local level. In addition, strict quality control procedures are essential in preparing composts for use in growing media [22].…”

“…The extensive use of peat as a basic and main component of substrates is due to relatively low costs in these areas, its excellent chemical, biological, and physical properties with low nutrient content, low pH, a unique combination of high water-holding capacity by high air space and drainage characteristics, light weight, and freedom from pests and diseases [14,16,21]. The unique microporous properties of Sphagnum peat and its resistance to degradation are matched by few other growing medium constituents [22].…”

Substitution of peat moss with softwood biochar for soil-free marigold growth

“…Such substrates typically have an inorganic and organic component (Bilderback et al, 2005). The organic component provides high porosity, low bulk density, and nutrient retention (e.g., water, nutrient ions) (Raviv et al, 1986), which makes Sphagnum peat moss a strongly suitable option with widespread use (Carlile et al, 2015;Robinson and Lamb, 1975). However, increasing expense and competing uses for peat (Caron et al, 2015), impacts of its harvest on wetland ecosystems (Barkham, 1993;Robertson, 1993), including loss of peat bogs as a key global C sink (Cleary et al, 2005), and its perception as unsustainable (Caron et al, 2015) have spurred recent investigations of substitutes for peat in soil-free substrates, including biomass waste products such as compost and sawdust (e.g., Ceglie et al, 2015;Maas and Adamson, 1972;Wright et al, 2009;Álvarez et al, 2017).…”

Organic Materials Used in Agriculture, Horticulture, Reconstructed Soils, and Filtering Applications

“…An important issue for the growing media industry is worldwide, economic, and environmental pressures to replace some constituents used in growing media mixes. In Carlile et al (2015), principal organic constituents of media and their properties are reviewed with particular attention to finding alternatives to peat, given concerns about environmental sustainability. The authors found that recent advances in the processing and quality control of coconut coir—a rapidly renewable product—make it a good alternative to peat.…”