GLENWOOD ORCHIDS pty ltd
COCONUT HUSK CHIPS AS AN ORCHID POTTING MEDIUM
In 2003 we began experimenting with a "new" potting medium for orchids called "Coconut Husk Chips" (CHCs or Coir), we now use it as our sole potting medium.
Our supplier was unable to provide any information on its use for orchids so we began our tests on a trial and error basis (mostly error!).
Our first tests with it failed dismally and we gave up until we received some further information that encouraged us to try again and to research the use of CHCs on the internet.
That produced a starting point from which we produced results that convinced us to try again in 2005.
As a result of further experimentation we now grow all of our stock in CHCs.
Initially we found a few negative reactions from our plants but lots of positives. The negatives were mainly due to CHCs preparation, not matching particle size to pot size for various genera and getting the water application rate correct.
The selection of the grade of chips and their preparation for use needs careful consideration and those new to its use will need to revise their watering habits, especially in very wet and very dry regions.
CHC's absorb more water than pine bark. A simple rule that is becoming apparent is ...."coarse in the bottom and small on top".
We have deflasked all the genera we grow into CHC's in various environmental conditions and we are continuing to monitor their progress.
Our weather conditions have varied greatly since our tests began - ranging between extremely dry to very wet during 2009.
Providing the plants have healthy root systems; try as we might to kill plants we have not done so yet. Watering and feeding routines will require some modification for some growers.
So...what are the methods we have evolved so far.
CHC GRADES AND QUALITY AVAILABLE
During 2007 CHC's have become available in various grades and qualities. The cheapest is an ungraded :multigrade. A premium grade is more expensive but very well graded and comes in a range of particle sizes. Each have their advantages.
For general use and for those with small collections of mixed genera, the cheaper multigrade packs have some advantages. We use both, but mostly the multigrade. The premium graded sizes are used mostly for few genera that need a very open substrate or those that will not tolerate "wet feet".
By sieving the multigrade we were getting a small amount of fines that we were discarding, until that is, we discovered Masdevallias could be grown in short fibres and some native terrestrials also would grow in the fines. The very fine particle "waste' material also had their uses in other areas such as a garden soil improver. We now waste nothing.
CHC's arrive in compressed dry blocks. To re-hydrate them each block is soaked in water which takes around 20 minutes if we are in a hurry. We add a cupful of hydrated lime (aka Ca OH, bricklayer's lime, hydrated lime) to each block then add nothing else except water. We have tested adding our normal strength liquid fertilizer during the final wash (about 1 litre per pack) and found no ill effects.
During our very dry 2008/09 summer when water was scarce we saved the wash water and used in on various trees and other garden plants with some very interesting results! So don't waste it!
If time, and water, is not a problem then we would suggest 3 changes of water is preferable to rid the chips of unwanted chemicals.
When completely expanded the CHC's are ready for use. For those with small collections the expanded material can dried and safely stored for future use; but they need to be re-wet before use. Don't pot into dry material (especially in hot weather).
Our main source of material is in the form of a "multigrade" product containing fines to coarse chips. The volume of fines and very coarse is fairly low. Our tests indicate that for our conditions the higher the air filled porosity (AFP) had produced better results. Root activity certainly has been proof of that. We also add coarser chips in the bottom third of the pot (appropriate for the pot size of course).
After plants have been repotted we water heavily on at least 3 occasions to flush unwanted natural chemical residues from the CHC's. We then apply calcium in the form of Calcium Hydroxide at regular intervals.
The particle size appears to be important for some genera. The chips will break down with age and watering. Only testing will help in deciding which is best for specific regions and growing environments.
There is no hard and fast rule as it will depend on plant size, pot size, how hot or dry ones growing environment is and the relevant orchid genus. We have had a severe water shortage for nearly 10 years and yet we have found no need to use fine grade material to increase the CHC's water holding capacity. In spite of the fact that during our driest and hottest summer (2009) when very severe water restrictions applied, we saw an a rush of spikes appearing once the heat vanished and rain fell.
One should allow for a breakdown of the material over a period of 1 to 2 years and the gradual reduction of medium air space, so the initial particle size can be slightly larger than expected. Trial and error is the only method of assessing the best size. If excess winter rain is a problem then a layer of very coarse chips in the bottom third of pots is a good solution.
If the cultural methods are correct root activity will compensate for that reduction.
Our feeding program is the same complete formula all year round. The NPK ratios are 21% N, 5% P, 16% K. Fe and Mg are higher than in most commercial products. We apply Calcium in the form of Ca OH (hydrated lime/calcium hydroxide) and we apply it when plants are growing vigorously (which in some cases is continuously) or are constantly moist. The frequency at which we apply Ca is around every 2 to 3 months.
We dust it over the foliage and potting mix then water it in.
If anyone suggests that Ca OH will harm orchids take a look at the Sarcochilus photo (above). All our Sarcs received a very heavy covering of it by accident and their response was to grow like mad.
CHC's apparently contain very high levels of Potassium (K) so we never apply extra or high K products.
The product we use is WestGro's Nutrisol and we have been using it for many years now and it works well with CHC's. We never use it in conjunction with other fertilizer products.
Growers will need to learn new watering habits. The easiest method is to lift pots and feel their weight at regular intervals. CHCs may appear very dry on top but can be very wet at the bottom.
Those growing small seedlings from flasks need to check the moisture content at the root zone until roots grow down into their pots. A layer of some fines on the surface can help as will regular misting for a few weeks.
A good rule to remember is that the surface of the pot will dry quickly while the bottom will stay wet. Try sticking you finger into your pots regularly to test the depth of the dryness, and lift pots here and there to become used to test the weight of pots. It does not hurt to carefully lift a plant from its pot to observe the condition of the roots. Using these tests you will soon learn how to control watering.
CHANGING FROM OTHER POTTING MEDIA
Plants with root damage will need some attention prior to repotting. All damaged, rotten and unhealthy roots must be removed along with any unneeded backbulbs. Plants must then be repotted into the smallest possible pot and left until fresh roots have developed sufficiently to allow repotting into a larger pot.
Repotting is easier than with bark. The CHCs shake off the roots very easily. A allow space for a more vigorous root system, and don't fill pot up to the top!
Vigorous root growth will soon push the plant upwards and beyond the top of the pot by as much as 50 mm! Don't pack it in tightly, just shake the pot vigorously to compact the chips.
Don't discard the used CHCs - they make excellent garden mulch!
One of our main original concerns before testing CHCs was whether we could use it for certain genera such as Sarcochilus.
The photo below is of a small Sarcochilus division planted into CHCs in February 2006 and removed from its pot around October 2006.
The plant had been grown continuously under shadecloth in our cold, wet winter conditions. During its test period it had received liberal applications of CaOH.
The new root development produced during that relatively short period is obvious.
The root condition on depotting was quite a surprise considering the size of the plant.
This response rate is now proving typical for every genera that we grow in CHC's - when we get all variables right!