Over the past two years we have had more rain than I can remember. I believe this has had a very detrimental effect on the pine bark being used as a potting medium. A few rumours are going round such as, that there is a fungus, which in these conditions is breaking down the bark quickly. However, commonsense tells you that any wood type product will decay at an accelerated rate under very constant wet and humid conditions we have had to endure.

From spring two years ago I realised my plants were experiencing abnormal problems from the bark. Very few which were repotted had adequate root systems because of the damage from their sodden bark potting mix. My initial response was to repot them into coarser bark, which had initial better results than the fine to medium grades I had been using. However, after six months or less the root systems quickly deteriorated again.
I came to the conclusion that it might be worthwhile trying a radically different medium to bark. I remembered that during the 70's there had been some experimentation with scoria, which is a red volcanic rock available from landscape suppliers. I had also through want of something to pot with planted a Dendrobium falcorostrum in pebbles (about 15mm) some five years previous. This plant in that time, without repotting, had grown into a magnificent specimen from just 3 canes. The pot was only 4" or 100mm in size. In fact I repotted this year for the first time in seven years to find a mass of healthy roots which you could not see the pebbles through. It was very impressive. So last March I began experimenting with Odontoglossums and Masdevallias. Half the plants were repotted in scoria, the other in pebbles about 15mm size. I was quickly delighted with their progress. The scoria is excellent for growing Masdevallia, Dracula etc., and I have a slight favour for the pebbles in regard to the Odontoglossums and Oncidiums. Saying that, plants in either have grown fantastic root systems and you can lift any plant by a leaf without fear of it falling out of its pot. Think of that with the added weight of scoria or pebbles over bark.

In fact the weight is probably the only disadvantage but not much of a problem for small plants.

In September last year I repotted nearly all my miscellaneous species and hybrids and nearly all my natives into scoria or pebble. I also for large pots or plants that would grow large used a new product called Absorbastone. Absorbastone weighs in at 18kg for a 50 litre bag (less weight than bark), and about the same price as bark. The progress on these plants in 99% of cases has been great. Having always been keen to grow plants to an absolute premium I am extremely pleased with the results to date.

In summing up, I believe I am still in an experimental stage with the growing mediums but they appear to be an excellent alternative for most epiphytic orchids. Ask this question; what natural orchid normally lives on radiata pine bark? I expect very few if any. Many orchids that are epiphytic however also live as lithophytes. I remember an impressive slide shown by A. B. Porter many years ago showing all sorts of species growing happily on a rock wall.

Rock and pebble type mediums have these properties

Advantages

• Low cost
• Very long lasting
• Excellent drainage
• Harmonious to the growth of most orchid root systems
• Less need to repot regularly (however some plants are growing so fast this might not be true).
• Should be easier to grow as specimens as less need to disturb root systems and root should grow better and more efficiently anyway.
• Pots rarely fall over in the wind.

Disadvantages

• Pots may be a fair bit heaver to carry.
• It would be more difficult to split plants when they become large.

I hope this small article gives you another idea, which may help, in growing your orchids. I think you will find in the case of most plants it worth giving a try. Happy orchid growing.

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