http://www.usu.edu/cpl/PDF/CoconutCoirPaper.pdfUSU CROP PHYSIOLOGY LABORATORY: RESEARCH: COCONUT COIR
A Comparison of Coconut Coir and Sphagnum Peat as Soil-less Media Components for Plant Growth
Jason Holman, B. Bugbee, and J. Chard - 2005
Coconut coir, a by-product of the coconut industry, has been promoted as an alternative to peat moss in soil-less media. Sphagnum peat moss has long been a standard component of soil-less media, but some people have expressed concern that it is a non-renewable resource. Although it does not appear that world peat resources will be in short supply for a very long time (see www.peatmoss.com), coconut coir may have characteristics that make it a useful component of soil-less media mixes. Coir has been considered to promote excellent plant growth but there are few rigorous studies that have compared it with peat moss control plants. However, ten years ago, Meerow (1994) found that growth of Ixora coccine was significantly reduced compared to growth in a sphagnum peat moss control. Vavrina (1996) found that there were no adverse effects of coir to tomato and pepper transplants, but a subsequent study in the same lab (Arenas et al., 2002) found that media with more than 50% coir had reduced growth compared to peat-grown control plants. They suggested that a high N immobilization by microorganisms and a high C:N ratio in the coir may have caused the reduced growth. Lopez-Galarza (2002) found that root development of strawberry plants grown in peat moss was better than in coir in some, but not all, studies. Handreck and Black (2002), in a comprehensive textbook on soil-less media, review the chemical and physical properties of coir dust that are being sold in Australia. They indicate that since all coir products have extremely high K contents and low Calcium contents, it is critical to add a source of Ca to improve plant calcium uptake. Since the pH is already close to 6, liming materials cannot be used because they would increase the pH above optimum. Handreck and Black says that “Therefore, all coir-based media must be amended with gypsum, which also overcomes their low sulfur status.” Ma and Nichols (2004) recently reported that the problems with coir extend beyond its high salinity. Their data indicate that high concentrations of phenolic compounds in fresh coir are at least partly responsible for the growth reductions observed in other studies. Several studies at the USU Crop Physiology Laboratory indicated that monocots grown in coconut coir were extremely chlorotic and stunted. The objective of this study was to see if there are differences among plant species and types of coconut coir compared to growth in sphagnum peat moss.
These studies show that coconut coir should be used with great caution. Although the Sri Lanka brands performed better than the Mexican brands, no brand performed consistently better than sphagnum peat. Some species tolerate coir better than others. The addition of calcium sulfate to the media did not have a consistently beneficial effect on growth and in some cases it reduced growth. The best growth in coir media occurred in the Grow Coir® brand. We are continuing these studies to determine the underlying causes of poor plant growth in coir.