In 1949, E. P. Hume wrote an article in the journal Economic Botany extolling the horticultural virtues of a by-product of the coconut husk fiber processing industry. Coir is the name given to the fibrous material that constitutes the thick mesocarp (middle layer) of the coconut fruit (Cocos nucifera). The long fibers of coir are extracted from the coconut husk and utilized in the manufacture of brushes, automobile seat and mattress stuffing, drainage pipe filters, twine and other products. Traditionally, the short fibers (2mm or less) and dust ("pith") left behind have accumulated as a waste product for which no industrial use had been discovered. Hume write of the excellent growth obtained with various plants when this coir dust or, as he called it, "cocopeat," was used as the growing medium (this word has now been registered as a trademark by one manufacturer of the material).

Hume was a prophet before his time. It is only in the last 10 years that his words of wisdom have percolated through the often conservative ways of international horticulture. In the 1970's and 80's, initial tests in Australia and Europe indicated that coir dust could function remarkably well as a substitute for various peat products in soilless container media for plant growth. Several Dutch companies have in fact been using coconut coir dust in production media since the 1980's, and the Royal Botanic Gardens at Kew is currently shifting most of its plant production into coir dust-based media. Sri Lanka (where over 2.5 billion coconut fruits are processed each year) has become the leading processor of what had previously been considered a waste product into a form suitable for horticultural use. While other sources may be available, companies in Sri Lanka have invested heavily in an infrastructure that guarantees consistency and quality of the product. Problems that can occur with coir dust where attention to quality control is not a priority include contamination with animal manures (with the attendant possibility of salmonella) and excess salinity. The former can be a problem in India, where cows often range free. The latter can occur anywhere where "green" coconuts are harvested for coir extraction. Unripe nuts are usually soaked in brine to make the fiber easier to extract, while fresh water is used with fully ripe coconuts.

Coir dust accumulates in large piles or "dumps" outside of the mills which process the husks for extraction of the industrially valuable long fibers. The high lignin and cellulose content of the pith prevents the piles from breaking down further. Some of the piles in Sri Lanka are reportedly a century old! It is this same characteristic that prevents oxidation and resultant shrinkage of coir dust when it is used as a growing medium.

As a product of wetland ecosystems, both sphagnum and sedge peat can't really be considered renewable resources at the level at which they are harvested from bogs and swamps to satisfy horticultural demand, despite claims made to the contrary by some industry representatives. Sedge peat (called "Florida peat" in that state), the less expensive of the two peats, is notorious for inconsistency in pH and quality. Sedge peat also has a tendency to breakdown quickly and sometimes loses volume after wetting. The superior (and much more expensive) sphagnum peat has shown wide swings in both price and availability in the last decade. Consequently, a high quality peat alternative that is consistently available and also satisfies heightened environmental concerns would be a "natural" in the marketplace. But can coir dust grow plants comparable in quality to sedge and sphagnum peat?

Coir dust is very similar to peat in appearance. It is light to dark brown in color and consists primarily of particles in the size range 0.2-2.0 mm (75-90%). Unlike sphagnum peat, there are no sticks or other extraneous matter.

Independent analyses of coir dust were performed in May and June 1991 at Auburn University, University of Arkansas, and A&L Analytical Laboratories (Memphis, TN). These results are summarized in Tables 1 and 2, and one manufacturer's technical data is also presented.

G. C. Cresswell (1992) looked at coir dust in comparison to sedge and sphagnum peat products and concluded that it has superior structural stability, water absorption ability and drainage, and cation exchange capacity compared to either sphagnum peat or sedge peat.

Coir dust tends to be high in both sodium and potassium (Table 2; Handreck, 1993) compared to the other peats, but Na is leached readily from the material under irrigation (Handreck, 1993). The high levels of potassium (Table 2) present in coir dust are interesting to note, and may actually prove more a benefit than any detriment to plant growth. Coir dust from sources other than Sri Lanka have also reportedly contained chlorides at levels toxic to many plants, thus it is very important that salinity in the raw material be monitored before processing into a horticultural amendment. It is evident, that chemical properties of this material can vary widely from source to source (Evans et al. 1996).

The higher pH of coir dust may allow less lime to be added to a coir dust-based medium, though adding dolomite to container soils is more important for Ca and Mg nutrition than for elevating pH. Cresswell did find that a small amount of nitrogen drawdown (N kept from availability to plants during decomposition of organic amendments low in nitrogen) occurred with coir dust, but typical production fertilization practices would likely compensate for the small amount of resulting N loss. At present, it is unclear how else fertilization regimes may need to be adjusted, if at all, in media composed chiefly of coir dust.

To date, few well designed tests have appeared assessing the performance of coir dust as a plant growth medium. The few technical reports, and the much larger anecdotal literature, are encouraging.

Cresswell (1992) compared coir dust to both sphagnum and sedge peat as a growing medium for broccoli, tomato and lettuce seedlings. He found earlier germination and greater size and uniformity of seedlings germinated and grown in coir dust. Handreck (1993) tested growth of Petunia x hybrida 'Celebrity Salmon' in 5.6:1 (v:v) mixes of either Malaysian coir dust, Sri Lankan coir dust, or a sphagnum from Sakhlin, Russia and silica sand. He observed equal growth when all three mixes were adjusted to pH 6 and total plant nutrients were supplied, but varying performance with changes in nutrient regime. He concluded that plants in coir dust-based media require more Ca, S, Cu and Fe, but less K, than those grown in peat. He also observed greater immobilization of soluble nitrogen with coir dust than peat, an observation confirmed by Cresswell (1992).

Trials at Whittle College in England with several woody ornamentals in various coir dust/bark blends indicated that coir dust performance was comparable to sphagnum peat. Unpublished technical reports from other institutions in England have indicated similar results with a wide range of greenhouse crops.

I tested the efficacy of coir dust as a peat substitute in replicated trials at the University of Florida Fort Lauderdale Research Center (Meerow, 1994, 1995). An ixora, an anthurium, majesty palm, and pentas were grown in container media that differed only in the peat fraction (40%). One mix utilized sphagnum, the second Florida (sedge) peat, and the third, coir dust. The pentas, ixora and majesty palm all grew much better in the coir dust mix than in sedge. Interestingly, the anthurium grew almost as well in the sedge peat mix as in the coir dust. The pentas, majesty palm and anthurium grew equally well in the coir dust medium as in the sphagnum medium. Only the anthurium showed slightly better top growth in the sphagnum mix, a factor I attributed to nitrogen lock-up by the coir dust.

The sedge peat-based medium had the greatest percent air space and the lowest water-holding capacity of the three media at the initiation of the trials, but at termination, showed considerable reversal of these parameters. The coir dust-based medium showed the least change in these parameters over time. The higher initial air porosity of the sedge-based medium may have been conducive to better initial root growth of the anthurium, as this plant is epiphytic in nature. No evidence of Cl or Na toxicity was observed on the plants in this study grown in the coir dust-based medium, and conductivity measurements indicated low levels of total dissolved salts.

More informally, I've noticed that seeds sown in a 1:1 (v:v) mix of coir dust and perlite seem to develop larger root systems than those germinated in 1:1 sphagnum and perlite. The material hold up very well under mist, and seems to support less algae growth than sphagnum. I've been further impressed by the ease with which coir dust re-wets after it has been thoroughly dehydrated. I found it takes about 3 hours to "fluff out" 20 bricks of 9:1 compressed coir dust. Claims have been made that coir dust is also slightly antibiotic, and thus may inhibit root pathogens, but this is, to my knowledge, undocumented.

Compared to Asia, there is little coir production in tropical America, and, consequently, low supplies of coir dust. Growing acceptance of the material in the horticultural marketplace is likely to change this, however, and we may see start-up companies in our own hemisphere attempting to compete with Sri Lanka in the future.

The following qualities of coir dust recommend its use as a peat substitute: 1) high water holding capacity equal or superior to sphagnum peat, 2) excellent drainage, equal to or better than sphagnum peat, 3) absence of weeds and pathogens, 4) greater physical resiliency (withstands compression of baling better) than sphagnum peat, 5) renewable resource; no ecological drawbacks to its use, 6) decomposes more slowly than sedge or sphagnum peat, 7) acceptable pH, cation exchange capacity and electrical conductivity, and 8) easier wetability than peat.

Coir dust may well be a product whose time has come. The key issues in developing widespread use of this material in American horticulture will be price (currently equal to sphagnum peat) and insuring consistent quality of the coir dusts that enter the marketplace (Evans et al. 1996).

Anonymous. 1992. Coir gets Kew seal of approval. Hort. Week 25(12): 3.

Balick, M. J. and H. T. Beck, eds. 1990. Useful Palms of the World. Columbia University Press, New York.

Barber, K. E. 1993. Peatlands as scientific archives of past biodiversity. Biodiv. Conserv. 2: 474-489

Barkham, J. P. 1993. For peat's sake: conservation or exploitation? Biodiv. Conserv. 2: 556-566.

Bragg, N. C. 1991. Peat and Its Alternatives. Horticultural Development Council, Petersfield.

Buckland, P. 1993. Peatland archaeology: a conservation resource on the edge of extinction. Biodiv. Conserv. 2: 513-527.

Bunt, A. C. 1988. Media and Mixes for Container-Grown Plants. Unwin Hyman, London.

Coghlan, A. 1992. Britain backs coconut composts. New Scientist 133: 26.

Cresswell, G. C. 1992. Coir dust - a viable alternative to peat? Pp. 1-5 in: Proceedings of the Australian Potting Mix Manufacturers Conference, Sydney.

Donelan, A. F. 1979. Use of coconut fibre waste in sugarcane seedling compost mixtures. Sugarcane Breeders' Newsl. 42: 1.

Evans, M. R., S. Konduru and R. H. Stamps. 1996. Source variation in physical and chemical properties of coconut cour dust. HortScience 31: 965-967.

Handreck, K. A. 1993. Properties of coir dust, and its use in the formulation of soilless potting media. Comm. Soil Sci. Plant Anal. 24: 349-363.

Hume. E. P. 1949. Coir dust or cocopeat - a by-product of the coconut. Economic Botany 3: 42-45.

Labey, B. 1991. Coir achieves peat performance. Hort. Week 24(18): 15.

Meerow, A. W. 1994. Growth of two subtropical ornamentals using coir dust (coconut mesocarp pith) as a peat substitute. HortScience 29: 1484-1486.

Meerow, A. W. 1995. Growth of two tropical foliage plants using coir dust as a container media amendment. HortTechnology :

Pryce, S. 1991. Alternatives to peat. Pro. Hortic. 5: 101-106.

Radjagukguk, B., A. Soekotjo, H. O. Soeseno and H. J. Santoso. 1983. A comparative study of peats and other media for containerised forest tree seedlings. Acta Hortic. 150: 449-458.

Reynolds, S. G. 1973. Preliminary studies in Western Samoa using various parts of the coconut palm (Cocos nucifera L.) as growing media. Acta Hortic. 37: 1983-1991.

Robertson, R. A. 1993. Peat, horticulture and environment. Biodiv. Conserv. 2: 541-547.

Smith, L. 1992. Unpublished report to Hensby Biotech Ltd. on tests with Novagrow, a coir-based container medium. Polytechnic of East London, Environment and Industry Research Unit.

Wehl, R. 1992. Unpublished report to ICI Garden Products on tests performed on various coir-based container media. Agrisearch UK. Ltd. Derbyshire, England.

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This report was prepared by Alan W. Meerow ( Associate Professor) Circa 1995

Coir Coconut Mesocarp Pith (Enviro-Coir) as a Peat Substitute
Alan W. Meerow
Palm and Tropical Ornamentals Specialist
Peat used in soilless container media for commercial plant production is harvested from wetland ecosystems at rates considered non-sustainable by wetland ecologists (Barber, 1993; Barkham, 1993; Buckland, 1993). While the peat industry argues that peatlands can be managed at sustainable levels (Robertson, 1993), it recognizes that alternatives to peat must be developed in order to meet environmental concerns of consumers and contend with increased regulation of peatland exploitation (Bragg, 1990; Robertson, 1993).
Previously (TropicLine 6(2): 1-4), I reported on the potential of coir dust (the short fibers and dust left behind after the industrially valuable long fibers of coir are extracted from the coconut husk) as a peat substitute. Here, I report on tests of coir dust as a 40% constituent in media for four ornamental crops: ixora, pentas, majesty palm, and anthurium.

Materials and Methods
In the first experiment, 30 liners of Ixora coccinea ‘Maui’ and Pentas lanceolata ‘Starburst Pink,’ and 20 liners of Anthurium ‘Lady Jane’ were potted into 3.7 liter containers of 5:4:1 (v:v) non-composted pine bark, either sedge peat or coir pith and sand on 13 Apr 1993.
Twenty-five liners of Ravenea rivularis (Majesty palm) were potted into 7.4 l containers of the same medium. In the second experiment, 15 liners of the same species were potted into 3.7 liter containers of 5:4:1 (v:v) non-composted pine bark, either sphagnum peat or coir pith and sand on 8 Aug 1993. All media were amended with 9.5 kg.m-3 Osmocote 17N-2.3P-10K, 4.16 kg.m-3 dolomite, and 1.2 kg.m-3 Micromax. Fifteen to thirty replicate plants, respectively for the two experiments, of each
treatment were arranged in a completely randomized design in full sun (max PPF=2100 umol.m-2.sec-1; ixora and pentas), 50% shade (majesty palm) or 63% shade (anthurium) and irrigated as necessary. Height and width measurements were taken at inception and again at termination from which a growth index was calculated (net change in height + net change in width). At termination, tops and roots were harvested, dried, and weighed. For the ixora and pentas, the first trials were terminated on 27 Jul 1993 (Pentas) and 7 Sep 1993 (Ixora); the second on 8 Nov 1993 (Pentas) and 4 Jan 1994 (Ixora). The anthuriums and majesty palms were harvested on 15 Dec 1993 (coir/sedge trials) and 4 Apr 1994 (coir/sphagnum trials).
Data were analyzed using ANOVA and Tukey’s Studentized Range test. Physical parameters, pH and conductivity (eC) of the media were determined at inception and again at termination for three replicate samples of each medium exposed to the same conditions as the plants, but in which no plant was grown. Measurement of pH and eC used the saturated paste extract method (Bunt, 1988).

Results
Pentas, ixora and majesty palm grown in coir-based media were superior in all growth parameters measured to those grown in sedge peat-based media (Table 1). The ixora in particular averaged nearly a fourfold, sixfold, and fivefold increase in growth index, top dry wt and root dry wt, respectively, in the coir-based medium as compared to sedge peat. The anthurium had significantly better top weight and growth index in the coir-based medium, but root dry weight equal in both sedge and coir-based medium. However, the differences in growth between sedge-grown anthurium and coir-grown anthurium were not as significant as with the other crops.
The sedge peat-based medium had the greatest per cent air space and the lowest water-holding capacity of the three media at the initiation of the trials but at termination, showed considerable reversal of these parameters (Table 3).
The coir-based medium showed the least change in these parameters over time.
There were no significant differences between growth, top or root dry weight of anthurium or majesty palm in coir-based vs. sphagnum peat-based media. Growth and top dry weights were similar for coir- and peat-grown pentas, but root dry weight was greater for coir-grown pentas plants (Table 2). The ixora had significantly greater growth and top dry weight in the sphagnum peat-based medium versus coir, but no difference in root dry weight (Table 2). These differences were not as large as observed between coir and sedge peat.
The better growth of ixora in sphagnum-based medium as compared to coir-based medium could have been due to nitrogen drawdown in the coir-based medium.

Conclusions
On the basis of plant growth parameters, coir pith was superior to sedge peat as a medium component (though only marginally for the anthurium) and at least equal to sphagnum peat for all crops tested except ixora. In this latter case, higher rates of nitrogen fertilization might have overcome the difference. The physical characteristics of coir pith appear more stable over time than either sedge peat or sphagnum peat.
For most plant producers in the United States, the primary decision on whether to use this material as a substitute for peat will likely be economic, and secondarily environmental. Sedge peat, despite its disadvantages, is very inexpensive relative to sphagnum. If high quality coir dust can be brought into the United States at a price competitive with sphagnum peat, it should find a ready market among users of the latter.
Literature Cited
Barber, K. E. 1993. Peatlands as scientific archives of past biodiversity. Biodiv. Conserv. 2: 474-489
Barkham, J. P. 1993. For peat’s sake: conservation or exploitation? Biodiv. Conserv. 2: 556-566
Bragg, N. C. 1991. Peat and Its Alternatives. Horticultural Development Council, Petersfield
Buckland, P. 1993. Peatland archaeology: a conservation resource on the edge of extinction.Biodiv. Conserv. 2: 513-527
Bunt, A. C. 1988. Media and Mixes for Container-Grown Plants. Unwin Hyman, London
Cresswell, G. C. 1992. Coir dust – a viable alternative to peat? Pp. 1-5 in: Proceedings of the Australian Potting Mix
Manufacturers Conference, Sydney
Pryce, S. 1991. Alternatives to peat. Pro. Hortic. 5: 101-106
Robertson, R. A. 1993. Peat, horticulture and environment. Biodiv. Conserv. 2: 541-547

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