Coconut Husk: An Alternative Potting Medium

by Terry Poulton and Rob & Noe Smith

For many years, pine bark has been the mainstay when it comes to potting mediums for most orchids in Australia, particularly for Cymbidiums. Used either as a sole ingredient, or in combination with other materials such as peat moss, perlite, isolite, rice hulls, peanut shells, etcetera, it has provided a stable medium suitable for most growing conditions and cultural regimes. Pine bark has provided orchid growers with a reliable and commonly available medium as it is a by-product of a long-term sustainable industry in this country. Bark has numerous advantages and a few disadvantages, but, on the whole, bark, particularly composted bark, has proven to be a convenient and reasonably cost effective medium for most genera.

This article is essentially intended as an introduction to a less well-known product now becoming more widely available in forms suitable for orchid culture – cocopeat or coconut husk. Trials and experiences both here and overseas indicate that it can provide a direct alternative to pine bark, or make a compatible addition to it as part of a more complex potting mix. Some commercial growers here and overseas have moved past trials to sustained use of this product.

In this article we have combined our own experiences trialing cocopeat in various forms with results achieved by others, including commercial orchid nurseries both here and in the USA, and with data from Australian and American distributors of the product. Hopefully in this way we can provide a comprehensive view of the material and its suitability as a potting medium for Cymbidiums and other orchid genera.

Some background information on the material and its production is appropriate, with the following information being sourced from both Australian and American suppliers (in this case, Galuku Cocopeat Australia and Sai Coir USA; anyone wishing to check out their comprehensive websites can go to www.cocopeat.com.au for Galuku, or www.saicocopeat.com for Sai Coir).

The product is made from essentially waste material generated by coconut farming in India and Sri Lanka, where some ten billion coconuts are produced each year. The thick fibrous husk (removed from the coconut as we know them in the shops) is made up of long fibres and sponge-like pith. We all know the most common products made from this material for many years – coir door mats and coir pot liners for hanging baskets – both made from the long tough fibres of the coconut's husk. Only around 20% of the husk is used for coir fibre extraction and is stored in large piles from two to four years, during which time it is weathered and leaching takes place. The next step in the process sees the long fibres removed, after which the product is dried in large concrete yards. A second screening removes short fibres prior to the material being compressed in hydraulic presses. The resultant blocks are tested for pH levels, salinity and any contaminants prior to storage and shipping.

The claimed properties for coir/cocopeat are high moisture retention, long-lasting (up to five years is claimed), that the moisture held is released slowly, good drainage, an ideal natural pH, that it is easy to re-wet, contains no weed seeds and is cost-effective and recyclable.

Galuku provides several grades, including fibre and chips (husk) in sizes 2mm to 6mm, a chip and short fibre combination, hydroponic slabs and blended products with trace elements for hydroponic use. Products suitable for orchid mixes are available in bales (20 x 40 x 33cm) weighing 20kg, compressed 3:1 and yielding 200 litres, in blocks yielding 60 litres and in briquettes.

For those concerned over the possible health risks from various potting media, the official Material Safety Data Sheet (MSDS) for the product in Australia lists no discernible health risks other than possible irritation to the airways if the dust is inhaled at high concentrations (typical of high levels of ingestion to the lungs of any fine material). Because the product is imported, it is also subject to Australian Quarantine rules and inspections. As the cocopeat is packed and shipped in compressed blocks and is immersed in water prior to use to reconstitute it, the risk from dust should be negligible if normal commonsense procedures are observed.

Before detailing our own experiences with cocopeat in its various forms as an orchid media, some particulars on experiences both here and overseas from a variety of commercial orchid nurseries may prove helpful! From the information we have been able to gather, the product has been in use by some growers in the USA for up to ten years and in Australia for as long as eight years; in all cases growers report favourable results with many mentions of improved growth – particularly that of root systems. Repeated references are made to the material's ability to last for four or five years in good condition. Growers both here and in America report good results with a variety of genera from Cymbidiums to Zygopetalums, Cattleyas, Paphiopedilums and numerous other genera. Among those giving favourable reports on cocopeat as a potting medium are Royale Orchids (NSW), one of Australia's premier nurseries (information supplied by Galuku Australia), Loren Bachman and Bob and Lyn Wellenstein in the USA. Bob and Lyn's AnTec Laboratories is a well-known and respected source of quality Paphiopedilum hybrids and species. They recommend cocopeat chips as their preferred medium for Paphs, being particularly impressed with "the speed of initiation and the number and substance of new roots".

Cymbidium Bark Mix

As far as our own trials and results are concerned, we will review our experiences and Terry's separately, as initially the tests were done in isolation of each other and without us knowing that Terry was experimenting with the same materials.

We began using the finely milled coir fibre product around five years ago. This is the material commonly available in briquettes in garden centres and supermarkets (NOT the briquettes with added fertiliser). The coir product was used to replace peat moss and rice hulls in our Cymbidium mix in a ratio of five parts bark, one part coir and one part canunda shell. Results indicated that the coir lasted in good condition for two or three years and would have lasted longer.

Some three years ago we switched to a slightly coarser version of the product available in larger blocks at a more economical price. Around two years ago we began trialing the cocopeat/coir chips and fibre available in compressed blocks which make up 60 litres when reconstituted. This medium was trialled in a variety of mixes, including as a sole medium, as a 50/50 mix with bark and as a 70% cocopeat, 20% bark, 10% canunda shell mix.

This last mix was the one we settled on as the most successful under our growing conditions. It appeared to promote healthy root development, good plant growth and avoid nitrogen draw-down as sometimes happens with freshly-potted Cymbidiums in pine bark. This combination also allowed us to maintain our normal watering and fertilising regime, as the plants were gradually moved across to the new mix following initial tests. All plants are watered overhead by an automatic system running on alternate days and once a week in winter. Feeding is via a top-dressing of Dynamic Lifter at moderated rates and fortnightly with quarter-strength liquid feed in summer with trace elements given as required.

One particular point we've noted using cocopeat is that the claims for water-holding properties without creating an overly wet mix seems to be accurate. If cocopeat chips are picked up a day after watering, they feel damp but not soggy; due to their make up a fair amount of water is held in their pithy structure and squeezing can release several drops of water from a single piece. In theory, the plant roots should be able to draw on this stored moisture effectively smoothing out the possible highs and lows of moisture availability between waterings. In terms of genera other than Cymbidiums, we have moved all of our Paphiopedilums into a mix of nine parts cocopeat to one part canunda shell. Following the reported results on the AnTec website, a few problem plants were trialled with such good results that all Paphs have now been moved into the new mix with encouraging results to date.

Other pluses we have found with cocopeat as a medium are ease of transport and storage (the blocks are easily stacked and take up less space than bags of bark). Cost is a major factor allowing for how much mix a reasonably-sized Cymbidium collection can take. At around $5.00 per 60 litres there's a considerable benefit involved.

In Terry's case, cocopeat in the chips/fibre form has been in trial for about two years with his Cymbidiums. The trials have involved its use under radically different growing conditions, yet the mix used is the same. Cocopeat chips have been trialled alone as a medium, cocopeat with coarse perlite added at ratios of both 50% and 10%, and also with composted bark in the same ratios. Having sourced cocopeat chips from two different suppliers, Terry has found that the size of the chips varies, one being quite coarse and the other being closer to medium-grade for pine bark (5-10mm approximately).

pH tests on the above media have produced some interesting results. pH levels for composted bark have proven to vary from batch to batch (depending on the degree of composting or, possibly, the quality of the bark harvested?), sometimes being as low as pH 4.0. When bark at pH 4.0 was combined 50/50 with cocopeat readings increased to around pH 5.5. With the addition of 'Rapid Raiser' (a product similar to Dynamic Lifter) pH levels were raised to around pH 7.0 in the 50/50 mix. At this level Terry has noted an increased rate of plant growth over those samples in the lower pH mixes. pH 4.0 bark use alone produced plants with slower growth and less root development, the roots being generally stumpy and brown-coloured. Root development in the mixes with 50% or more of cocopeat were thicker, often branched and had large healthy white growing tips. The two sets of growing conditions Terry has trialled his Cymbidiums in the cocopeat mixes are as follows:

To date, Terry reports no significant problems with any of the cocopeat trial mixes during a Victorian winter; although, as with our own tests, all plants are protected from the variances of natural rainfall. Anyone contemplating cocopeat-based mediums under shade cloth would be well advised to run some trials of their own before making a wholesale change. So far, the results seen by Terry and ourselves match the results reported by Australian and American commercial growers using the medium and also match the claims made by the various distributors.

We source our cocopeat/coir chips from David Francis' company Duralite, located in Heatherton, Victoria, who distributes the Galuku product. Agents in other states can be sourced through Galuku. As mentioned earlier in this article, be aware that some cocopeat blocks and briquettes sold though garden centres and supermarkets contain added fertiliser and are probably unsuitable for Cymbidiums and other orchid genera as they are formulated more for gross feeding bedding type plants.

While cocopeat seems to have a lot going for it as a Cymbidium medium and the maintenance of reliable quality-controlled supplies should be sustainable given the size of the industry that generates it and the long life to date of other coconut/coir products, no one is claiming cocopeat to be a new "miracle" potting mix (has there ever been any such thing?). What tests seem to prove is that it is a reliable, convenient, low-cost option which allows good plant growth and aids with root development IF you get your basic culture right. NO mix, special fertiliser, or any other single thing can work if good culture in all other areas is neglected – get the basics right and these products may give a little extra to your overall success.

Remember to do some tests of your own before making a total change. Good luck and good growing!

Terry Poulton
Rob and Noe Smith