Coir Dust, A Viable Alternative to Peat Moss

Alan W. Meerow
Associate Professor

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?

Physical & Chemical Characteristics

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.

Performance of Coir dust as a Plant Growth Medium

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.

Availability of Coir dust

Sri Lankan coir dust is available in bulk from several sources in the United States and Canada at this time. Lignocell Co. (P.O. Box 7921, The Woodlands, TX 77387) processes the pith into highly compressed bricks (9:1; the company may now have switched to a lower compression ratio) approximately 7.9" X 3.9" x 1.9" in size, each weighing approximately 1.5 lbs. For commercial growers, the bricks are packed into shrink-wrapped pallets of 2050 bricks (for retail sale, shrink-wrapped 12-brick packages weighing 17 lbs. and equipped with handle are available). A bulk pallet of 2050 blocks measures 7.3' tall x 3.5' wide x 3.8' long, weighs 3000 lbs and will supposedly yield as much material when re-wet as 128 4-cu. ft. bales of peat moss, but takes up a fraction of the storage space. Twelve bricks "fluff out" when re-wet into about 4 cu. ft. of ready-to-use material. Approximately 2 gallons of water is required per brick. Similar products are available from GrowCoir, INC., P. O. Box 154516, Waco, TX 76715, (817) 822-1577; Florikan, 1523 Edger Place, Sarasota, FL 34240, (800) 552-8666; Tierra Associates, 801 Portola Dr. 202, San Fransisco, CA 94127, (415) 566-4092; and Green Soils, LTD, Canada, (416) 494-9810, (905) 949-4679. Applied Environmental Technologies (2017 Country Ridge Place, Birmingham, AL 35243) sells a 5:1 compressed bale of coir dust approximately 27.5" x 14.2" x 5.5." Their bale requires about 15 gallons of water for rehydration and will yield about 5 cubic feet of material.

Scotts, Inc. has begun to offer commercial horticultural media containing coir dust. Local soil mix companies in Florida have been reluctant to offer coir dust until it can be processed exactly as they do sphagnum peat. I've found that local companies charge a premium to rehydrate the bales of coir dust and incorporate the material into a custom medium.

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 and the Philippines 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).

References and Further Reading

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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Table 1. Properties of various coir dusts, * * = not reported.


            Property          
 

pH

%WHCy

%TPSy

%ASy

CEC

eCx

%TOM

%OC

C:N

%L

%C

Source

           

* *

* *

* *

* *

* *

1

4.97

* *

* *

* *

* *

1.30

* *

* *

* *

* *

* *

 

4.98

       

1.3

* *

* *

* *

* *

* *

2

4.9

64.5

79.8

15.3

83.7v

0.87

* *

* *

* *

* *

* *

 

5.0

66.1

81.7

15.6

85.4v

1.43

* *

* *

* *

* *

* *

3

4.8

* *

* *

* *

* *

1.80

* *

* *

* *

* *

* *

4

5.4-6.8

8-9 times dry weight

94-96

10-12

60-130v

2.5 max

94-98

45-50

80:1

65-70

25-30

5

5.5

* *

* *

* *

21u

0.8

* *

* *

* *

* *

* *

 

5.7

     

30u

1.9

* *

* *

* *

* *

* *

______________________

z%WHC = % water holding capacity, %TPS = % total porosity, %AS = % air space, CEC = cation exchange capacity, eC = conductivity, %TOM = % total organic matter (wt./wt., dry basis), %OC = % organic carbon (wt./wt., dry basis), C:N = carbon: nitrogen ratio, %L = % lignin, %C = % cellulose

ycolumn height unreported

xdS/m

w1 = Auburn University Soil Testing Laboratory, 7 Jun 91; 2 = A&L Laboratories (Memphis, TN), 19 Jun 91; 3 = University of Arkansas Soil Testing Laboratory, 1 May 92; 4 = EZ Soil Co. data; 5 = Handreck (1993). All data except Handreck (1993) based on Lignocell coir dust.

vmeq/100 gm, dry basis

umeq/l


Table 2. Chemical properties of various coir dusts (DPTA extractions of saturated media extract, ppm), * * = not reported.


              Element                
Sourcez N (NO3) N (NH4) P K Ca Mg S Mn Fe B Zn Cu Cl- Na Al
1 2.22 * * 10 308 3 4 * * * * * * * * * * * * * * * * * *
  2.46 * * 10 290 2 4 * * * * * * * * * * * * * * * * * *
2 2 2 8 172 4 3 33 0.1 0.5 1.0 0.07 0.03 * * 61 < 1
  1 2 6 271 2 4 10 0.1 0.4 0.1 0.11 0.04 * * 104 < 1
3 10.4 * * 8.5 319 3.9 4.6 * * * * 0.9 * * 0.3 0.1 * * 105 * *
4 0 0 17 720 15 28 8 1.5 5 0.18 0.3 0.22 886 110 * *
  9 0 8 304 6 8 2 1.1 7 0.12 1.3 0.17 250 114 * *
                      0.7       * *

__________________________

z1 = Auburn University Soil Testing Laboratory, 7 Jun 91; 2 = A&L Laboratories (Memphis, TN), 19 Jun 91; 3 = University of Arkansas Soil Testing Laboratory, 1 May 92; 4 = Handreck (1993). All data except Handreck (1993) based on Lignocell coir dust.